diff --git a/googlemock/README.md b/googlemock/README.md index 6465fc6a..36f87761 100644 --- a/googlemock/README.md +++ b/googlemock/README.md @@ -1,206 +1,206 @@ ## Google Mock ## The Google C++ mocking framework. ### Overview ### Google's framework for writing and using C++ mock classes. It can help you derive better designs of your system and write better tests. It is inspired by: * [jMock](http://www.jmock.org/), * [EasyMock](http://www.easymock.org/), and * [Hamcrest](http://code.google.com/p/hamcrest/), and designed with C++'s specifics in mind. Google mock: * lets you create mock classes trivially using simple macros. * supports a rich set of matchers and actions. * handles unordered, partially ordered, or completely ordered expectations. * is extensible by users. We hope you find it useful! ### Features ### * Provides a declarative syntax for defining mocks. * Can easily define partial (hybrid) mocks, which are a cross of real and mock objects. * Handles functions of arbitrary types and overloaded functions. * Comes with a rich set of matchers for validating function arguments. * Uses an intuitive syntax for controlling the behavior of a mock. * Does automatic verification of expectations (no record-and-replay needed). * Allows arbitrary (partial) ordering constraints on function calls to be expressed,. * Lets a user extend it by defining new matchers and actions. * Does not use exceptions. * Is easy to learn and use. Please see the project page above for more information as well as the mailing list for questions, discussions, and development. There is also an IRC channel on OFTC (irc.oftc.net) #gtest available. Please join us! Please note that code under [scripts/generator](scripts/generator/) is from [cppclean](http://code.google.com/p/cppclean/) and released under the Apache License, which is different from Google Mock's license. ## Getting Started ## If you are new to the project, we suggest that you read the user documentation in the following order: * Learn the [basics](../googletest/docs/primer.md) of Google Test, if you choose to use Google Mock with it (recommended). - * Read [Google Mock for Dummies](../googlemock/docs/ForDummies.md). + * Read [Google Mock for Dummies](../googlemock/docs/for_dummies.md). * Read the instructions below on how to build Google Mock. You can also watch Zhanyong's [talk](http://www.youtube.com/watch?v=sYpCyLI47rM) on Google Mock's usage and implementation. Once you understand the basics, check out the rest of the docs: - * [CheatSheet](../googlemock/docs/CheatSheet.md) - all the commonly used stuff + * [CheatSheet](../googlemock/docs/cheat_sheet.md) - all the commonly used stuff at a glance. * [CookBook](../googlemock/docs/cook_book.md) - recipes for getting things done, including advanced techniques. If you need help, please check the -[KnownIssues](docs/KnownIssues.md) and -[FrequentlyAskedQuestions](docs/FrequentlyAskedQuestions.md) before +[KnownIssues](docs/known_issues.md) and +[FrequentlyAskedQuestions](docs/frequently_asked_questions.md) before posting a question on the [discussion group](http://groups.google.com/group/googlemock). ### Using Google Mock Without Google Test ### Google Mock is not a testing framework itself. Instead, it needs a testing framework for writing tests. Google Mock works seamlessly with [Google Test](https://github.com/google/googletest), but -you can also use it with [any C++ testing framework](../googlemock/docs/ForDummies.md#using-google-mock-with-any-testing-framework). +you can also use it with [any C++ testing framework](../googlemock/docs/for_dummies.md#using-google-mock-with-any-testing-framework). ### Requirements for End Users ### Google Mock is implemented on top of [Google Test]( http://github.com/google/googletest/), and depends on it. You must use the bundled version of Google Test when using Google Mock. You can also easily configure Google Mock to work with another testing framework, although it will still need Google Test. Please read ["Using_Google_Mock_with_Any_Testing_Framework"]( - ../googlemock/docs/ForDummies.md#using-google-mock-with-any-testing-framework) + ../googlemock/docs/for_dummies.md#using-google-mock-with-any-testing-framework) for instructions. Google Mock depends on advanced C++ features and thus requires a more modern compiler. The following are needed to use Google Mock: #### Linux Requirements #### * GNU-compatible Make or "gmake" * POSIX-standard shell * POSIX(-2) Regular Expressions (regex.h) * C++98-standard-compliant compiler (e.g. GCC 3.4 or newer) #### Windows Requirements #### * Microsoft Visual C++ 8.0 SP1 or newer #### Mac OS X Requirements #### * Mac OS X 10.4 Tiger or newer * Developer Tools Installed ### Requirements for Contributors ### We welcome patches. If you plan to contribute a patch, you need to build Google Mock and its tests, which has further requirements: * Automake version 1.9 or newer * Autoconf version 2.59 or newer * Libtool / Libtoolize * Python version 2.3 or newer (for running some of the tests and re-generating certain source files from templates) ### Building Google Mock ### #### Using CMake #### If you have CMake available, it is recommended that you follow the [build instructions][gtest_cmakebuild] as described for Google Test. If are using Google Mock with an existing CMake project, the section [Incorporating Into An Existing CMake Project][gtest_incorpcmake] may be of particular interest. To make it work for Google Mock you will need to change target_link_libraries(example gtest_main) to target_link_libraries(example gmock_main) This works because `gmock_main` library is compiled with Google Test. ### Tweaking Google Mock ### Google Mock can be used in diverse environments. The default configuration may not work (or may not work well) out of the box in some environments. However, you can easily tweak Google Mock by defining control macros on the compiler command line. Generally, these macros are named like `GTEST_XYZ` and you define them to either 1 or 0 to enable or disable a certain feature. We list the most frequently used macros below. For a complete list, see file [${GTEST\_DIR}/include/gtest/internal/gtest-port.h]( ../googletest/include/gtest/internal/gtest-port.h). ### As a Shared Library (DLL) ### Google Mock is compact, so most users can build and link it as a static library for the simplicity. Google Mock can be used as a DLL, but the same DLL must contain Google Test as well. See [Google Test's README][gtest_readme] for instructions on how to set up necessary compiler settings. ### Tweaking Google Mock ### Most of Google Test's control macros apply to Google Mock as well. Please see [Google Test's README][gtest_readme] for how to tweak them. ### Upgrading from an Earlier Version ### We strive to keep Google Mock releases backward compatible. Sometimes, though, we have to make some breaking changes for the users' long-term benefits. This section describes what you'll need to do if you are upgrading from an earlier version of Google Mock. #### Upgrading from 1.1.0 or Earlier #### You may need to explicitly enable or disable Google Test's own TR1 tuple library. See the instructions in section "[Choosing a TR1 Tuple Library](#choosing-a-tr1-tuple-library)". #### Upgrading from 1.4.0 or Earlier #### On platforms where the pthread library is available, Google Test and Google Mock use it in order to be thread-safe. For this to work, you may need to tweak your compiler and/or linker flags. Please see the "[Multi-threaded Tests](../googletest/README.md#multi-threaded-tests)" section in file Google Test's README for what you may need to do. If you have custom matchers defined using `MatcherInterface` or `MakePolymorphicMatcher()`, you'll need to update their definitions to use the new matcher API ( [monomorphic](./docs/cook_book.md#writing-new-monomorphic-matchers), [polymorphic](./docs/cook_book.md#writing-new-polymorphic-matchers)). Matchers defined using `MATCHER()` or `MATCHER_P*()` aren't affected. Happy testing! [gtest_readme]: ../googletest/README.md "googletest" [gtest_cmakebuild]: ../googletest/README.md#using-cmake "Using CMake" [gtest_incorpcmake]: ../googletest/README.md#incorporating-into-an-existing-cmake-project "Incorporating Into An Existing CMake Project" diff --git a/googlemock/docs/CheatSheet.md b/googlemock/docs/cheat_sheet.md similarity index 100% rename from googlemock/docs/CheatSheet.md rename to googlemock/docs/cheat_sheet.md diff --git a/googlemock/docs/cook_book.md b/googlemock/docs/cook_book.md index 8f26a839..d0402091 100644 --- a/googlemock/docs/cook_book.md +++ b/googlemock/docs/cook_book.md @@ -1,3660 +1,3660 @@ ## Google Mock Cookbook You can find recipes for using Google Mock here. If you haven't yet, -please read the [ForDummies](ForDummies.md) document first to make sure you understand +please read the [ForDummies](for_dummies.md) document first to make sure you understand the basics. **Note:** Google Mock lives in the `testing` name space. For readability, it is recommended to write `using ::testing::Foo;` once in your file before using the name `Foo` defined by Google Mock. We omit such `using` statements in this page for brevity, but you should do it in your own code. # Creating Mock Classes # ## Mocking Private or Protected Methods ## You must always put a mock method definition (`MOCK_METHOD*`) in a `public:` section of the mock class, regardless of the method being mocked being `public`, `protected`, or `private` in the base class. This allows `ON_CALL` and `EXPECT_CALL` to reference the mock function from outside of the mock class. (Yes, C++ allows a subclass to specify a different access level than the base class on a virtual function.) Example: ```cpp class Foo { public: ... virtual bool Transform(Gadget* g) = 0; protected: virtual void Resume(); private: virtual int GetTimeOut(); }; class MockFoo : public Foo { public: ... MOCK_METHOD1(Transform, bool(Gadget* g)); // The following must be in the public section, even though the // methods are protected or private in the base class. MOCK_METHOD0(Resume, void()); MOCK_METHOD0(GetTimeOut, int()); }; ``` ## Mocking Overloaded Methods ## You can mock overloaded functions as usual. No special attention is required: ```cpp class Foo { ... // Must be virtual as we'll inherit from Foo. virtual ~Foo(); // Overloaded on the types and/or numbers of arguments. virtual int Add(Element x); virtual int Add(int times, Element x); // Overloaded on the const-ness of this object. virtual Bar& GetBar(); virtual const Bar& GetBar() const; }; class MockFoo : public Foo { ... MOCK_METHOD1(Add, int(Element x)); MOCK_METHOD2(Add, int(int times, Element x)); MOCK_METHOD0(GetBar, Bar&()); MOCK_CONST_METHOD0(GetBar, const Bar&()); }; ``` **Note:** if you don't mock all versions of the overloaded method, the compiler will give you a warning about some methods in the base class being hidden. To fix that, use `using` to bring them in scope: ```cpp class MockFoo : public Foo { ... using Foo::Add; MOCK_METHOD1(Add, int(Element x)); // We don't want to mock int Add(int times, Element x); ... }; ``` ## Mocking Class Templates ## To mock a class template, append `_T` to the `MOCK_*` macros: ```cpp template class StackInterface { ... // Must be virtual as we'll inherit from StackInterface. virtual ~StackInterface(); virtual int GetSize() const = 0; virtual void Push(const Elem& x) = 0; }; template class MockStack : public StackInterface { ... MOCK_CONST_METHOD0_T(GetSize, int()); MOCK_METHOD1_T(Push, void(const Elem& x)); }; ``` ## Mocking Nonvirtual Methods ## Google Mock can mock non-virtual functions to be used in what we call _hi-perf dependency injection_. In this case, instead of sharing a common base class with the real class, your mock class will be _unrelated_ to the real class, but contain methods with the same signatures. The syntax for mocking non-virtual methods is the _same_ as mocking virtual methods: ```cpp // A simple packet stream class. None of its members is virtual. class ConcretePacketStream { public: void AppendPacket(Packet* new_packet); const Packet* GetPacket(size_t packet_number) const; size_t NumberOfPackets() const; ... }; // A mock packet stream class. It inherits from no other, but defines // GetPacket() and NumberOfPackets(). class MockPacketStream { public: MOCK_CONST_METHOD1(GetPacket, const Packet*(size_t packet_number)); MOCK_CONST_METHOD0(NumberOfPackets, size_t()); ... }; ``` Note that the mock class doesn't define `AppendPacket()`, unlike the real class. That's fine as long as the test doesn't need to call it. Next, you need a way to say that you want to use `ConcretePacketStream` in production code and to use `MockPacketStream` in tests. Since the functions are not virtual and the two classes are unrelated, you must specify your choice at _compile time_ (as opposed to run time). One way to do it is to templatize your code that needs to use a packet stream. More specifically, you will give your code a template type argument for the type of the packet stream. In production, you will instantiate your template with `ConcretePacketStream` as the type argument. In tests, you will instantiate the same template with `MockPacketStream`. For example, you may write: ```cpp template void CreateConnection(PacketStream* stream) { ... } template class PacketReader { public: void ReadPackets(PacketStream* stream, size_t packet_num); }; ``` Then you can use `CreateConnection()` and `PacketReader` in production code, and use `CreateConnection()` and `PacketReader` in tests. ```cpp MockPacketStream mock_stream; EXPECT_CALL(mock_stream, ...)...; .. set more expectations on mock_stream ... PacketReader reader(&mock_stream); ... exercise reader ... ``` ## Mocking Free Functions ## It's possible to use Google Mock to mock a free function (i.e. a C-style function or a static method). You just need to rewrite your code to use an interface (abstract class). Instead of calling a free function (say, `OpenFile`) directly, introduce an interface for it and have a concrete subclass that calls the free function: ```cpp class FileInterface { public: ... virtual bool Open(const char* path, const char* mode) = 0; }; class File : public FileInterface { public: ... virtual bool Open(const char* path, const char* mode) { return OpenFile(path, mode); } }; ``` Your code should talk to `FileInterface` to open a file. Now it's easy to mock out the function. This may seem much hassle, but in practice you often have multiple related functions that you can put in the same interface, so the per-function syntactic overhead will be much lower. If you are concerned about the performance overhead incurred by virtual functions, and profiling confirms your concern, you can combine this with the recipe for [mocking non-virtual methods](#mocking-nonvirtual-methods). ## The Nice, the Strict, and the Naggy ## If a mock method has no `EXPECT_CALL` spec but is called, Google Mock will print a warning about the "uninteresting call". The rationale is: * New methods may be added to an interface after a test is written. We shouldn't fail a test just because a method it doesn't know about is called. * However, this may also mean there's a bug in the test, so Google Mock shouldn't be silent either. (Note that the user should [*not* add an `EXPECT_CALL()`](https://github.com/google/googletest/blob/master/googlemock/docs/CookBook.md#knowing-when-to-expect) to suppress the warning, even if they think the call is harmless). However, sometimes you may want to suppress all "uninteresting call" warnings, while sometimes you may want the opposite, i.e. to treat all of them as errors. Google Mock lets you make the decision on a per-mock-object basis. Suppose your test uses a mock class `MockFoo`: ```cpp TEST(...) { MockFoo mock_foo; EXPECT_CALL(mock_foo, DoThis()); ... code that uses mock_foo ... } ``` If a method of `mock_foo` other than `DoThis()` is called, it will be reported by Google Mock as a warning. However, if you rewrite your test to use `NiceMock` instead, the warning will be gone, resulting in a cleaner test output: ```cpp using ::testing::NiceMock; TEST(...) { NiceMock mock_foo; EXPECT_CALL(mock_foo, DoThis()); ... code that uses mock_foo ... } ``` `NiceMock` is a subclass of `MockFoo`, so it can be used wherever `MockFoo` is accepted. It also works if `MockFoo`'s constructor takes some arguments, as `NiceMock` "inherits" `MockFoo`'s constructors: ```cpp using ::testing::NiceMock; TEST(...) { NiceMock mock_foo(5, "hi"); // Calls MockFoo(5, "hi"). EXPECT_CALL(mock_foo, DoThis()); ... code that uses mock_foo ... } ``` The usage of `StrictMock` is similar, except that it makes all uninteresting calls failures: ```cpp using ::testing::StrictMock; TEST(...) { StrictMock mock_foo; EXPECT_CALL(mock_foo, DoThis()); ... code that uses mock_foo ... // The test will fail if a method of mock_foo other than DoThis() // is called. } ``` There are some caveats though (I don't like them just as much as the next guy, but sadly they are side effects of C++'s limitations): 1. `NiceMock` and `StrictMock` only work for mock methods defined using the `MOCK_METHOD*` family of macros **directly** in the `MockFoo` class. If a mock method is defined in a **base class** of `MockFoo`, the "nice" or "strict" modifier may not affect it, depending on the compiler. In particular, nesting `NiceMock` and `StrictMock` (e.g. `NiceMock >`) is **not** supported. 1. The constructors of the base mock (`MockFoo`) cannot have arguments passed by non-const reference, which happens to be banned by the [Google C++ style guide](https://google.github.io/styleguide/cppguide.html). 1. During the constructor or destructor of `MockFoo`, the mock object is _not_ nice or strict. This may cause surprises if the constructor or destructor calls a mock method on `this` object. (This behavior, however, is consistent with C++'s general rule: if a constructor or destructor calls a virtual method of `this` object, that method is treated as non-virtual. In other words, to the base class's constructor or destructor, `this` object behaves like an instance of the base class, not the derived class. This rule is required for safety. Otherwise a base constructor may use members of a derived class before they are initialized, or a base destructor may use members of a derived class after they have been destroyed.) Finally, you should be **very cautious** about when to use naggy or strict mocks, as they tend to make tests more brittle and harder to maintain. When you refactor your code without changing its externally visible behavior, ideally you should't need to update any tests. If your code interacts with a naggy mock, however, you may start to get spammed with warnings as the result of your change. Worse, if your code interacts with a strict mock, your tests may start to fail and you'll be forced to fix them. Our general recommendation is to use nice mocks (not yet the default) most of the time, use naggy mocks (the current default) when developing or debugging tests, and use strict mocks only as the last resort. ## Simplifying the Interface without Breaking Existing Code ## Sometimes a method has a long list of arguments that is mostly uninteresting. For example, ```cpp class LogSink { public: ... virtual void send(LogSeverity severity, const char* full_filename, const char* base_filename, int line, const struct tm* tm_time, const char* message, size_t message_len) = 0; }; ``` This method's argument list is lengthy and hard to work with (let's say that the `message` argument is not even 0-terminated). If we mock it as is, using the mock will be awkward. If, however, we try to simplify this interface, we'll need to fix all clients depending on it, which is often infeasible. The trick is to re-dispatch the method in the mock class: ```cpp class ScopedMockLog : public LogSink { public: ... virtual void send(LogSeverity severity, const char* full_filename, const char* base_filename, int line, const tm* tm_time, const char* message, size_t message_len) { // We are only interested in the log severity, full file name, and // log message. Log(severity, full_filename, std::string(message, message_len)); } // Implements the mock method: // // void Log(LogSeverity severity, // const string& file_path, // const string& message); MOCK_METHOD3(Log, void(LogSeverity severity, const string& file_path, const string& message)); }; ``` By defining a new mock method with a trimmed argument list, we make the mock class much more user-friendly. ## Alternative to Mocking Concrete Classes ## Often you may find yourself using classes that don't implement interfaces. In order to test your code that uses such a class (let's call it `Concrete`), you may be tempted to make the methods of `Concrete` virtual and then mock it. Try not to do that. Making a non-virtual function virtual is a big decision. It creates an extension point where subclasses can tweak your class' behavior. This weakens your control on the class because now it's harder to maintain the class' invariants. You should make a function virtual only when there is a valid reason for a subclass to override it. Mocking concrete classes directly is problematic as it creates a tight coupling between the class and the tests - any small change in the class may invalidate your tests and make test maintenance a pain. To avoid such problems, many programmers have been practicing "coding to interfaces": instead of talking to the `Concrete` class, your code would define an interface and talk to it. Then you implement that interface as an adaptor on top of `Concrete`. In tests, you can easily mock that interface to observe how your code is doing. This technique incurs some overhead: * You pay the cost of virtual function calls (usually not a problem). * There is more abstraction for the programmers to learn. However, it can also bring significant benefits in addition to better testability: * `Concrete`'s API may not fit your problem domain very well, as you may not be the only client it tries to serve. By designing your own interface, you have a chance to tailor it to your need - you may add higher-level functionalities, rename stuff, etc instead of just trimming the class. This allows you to write your code (user of the interface) in a more natural way, which means it will be more readable, more maintainable, and you'll be more productive. * If `Concrete`'s implementation ever has to change, you don't have to rewrite everywhere it is used. Instead, you can absorb the change in your implementation of the interface, and your other code and tests will be insulated from this change. Some people worry that if everyone is practicing this technique, they will end up writing lots of redundant code. This concern is totally understandable. However, there are two reasons why it may not be the case: * Different projects may need to use `Concrete` in different ways, so the best interfaces for them will be different. Therefore, each of them will have its own domain-specific interface on top of `Concrete`, and they will not be the same code. * If enough projects want to use the same interface, they can always share it, just like they have been sharing `Concrete`. You can check in the interface and the adaptor somewhere near `Concrete` (perhaps in a `contrib` sub-directory) and let many projects use it. You need to weigh the pros and cons carefully for your particular problem, but I'd like to assure you that the Java community has been practicing this for a long time and it's a proven effective technique applicable in a wide variety of situations. :-) ## Delegating Calls to a Fake ## Some times you have a non-trivial fake implementation of an interface. For example: ```cpp class Foo { public: virtual ~Foo() {} virtual char DoThis(int n) = 0; virtual void DoThat(const char* s, int* p) = 0; }; class FakeFoo : public Foo { public: virtual char DoThis(int n) { return (n > 0) ? '+' : (n < 0) ? '-' : '0'; } virtual void DoThat(const char* s, int* p) { *p = strlen(s); } }; ``` Now you want to mock this interface such that you can set expectations on it. However, you also want to use `FakeFoo` for the default behavior, as duplicating it in the mock object is, well, a lot of work. When you define the mock class using Google Mock, you can have it delegate its default action to a fake class you already have, using this pattern: ```cpp using ::testing::_; using ::testing::Invoke; class MockFoo : public Foo { public: // Normal mock method definitions using Google Mock. MOCK_METHOD1(DoThis, char(int n)); MOCK_METHOD2(DoThat, void(const char* s, int* p)); // Delegates the default actions of the methods to a FakeFoo object. // This must be called *before* the custom ON_CALL() statements. void DelegateToFake() { ON_CALL(*this, DoThis(_)) .WillByDefault(Invoke(&fake_, &FakeFoo::DoThis)); ON_CALL(*this, DoThat(_, _)) .WillByDefault(Invoke(&fake_, &FakeFoo::DoThat)); } private: FakeFoo fake_; // Keeps an instance of the fake in the mock. }; ``` With that, you can use `MockFoo` in your tests as usual. Just remember that if you don't explicitly set an action in an `ON_CALL()` or `EXPECT_CALL()`, the fake will be called upon to do it: ```cpp using ::testing::_; TEST(AbcTest, Xyz) { MockFoo foo; foo.DelegateToFake(); // Enables the fake for delegation. // Put your ON_CALL(foo, ...)s here, if any. // No action specified, meaning to use the default action. EXPECT_CALL(foo, DoThis(5)); EXPECT_CALL(foo, DoThat(_, _)); int n = 0; EXPECT_EQ('+', foo.DoThis(5)); // FakeFoo::DoThis() is invoked. foo.DoThat("Hi", &n); // FakeFoo::DoThat() is invoked. EXPECT_EQ(2, n); } ``` **Some tips:** * If you want, you can still override the default action by providing your own `ON_CALL()` or using `.WillOnce()` / `.WillRepeatedly()` in `EXPECT_CALL()`. * In `DelegateToFake()`, you only need to delegate the methods whose fake implementation you intend to use. * The general technique discussed here works for overloaded methods, but you'll need to tell the compiler which version you mean. To disambiguate a mock function (the one you specify inside the parentheses of `ON_CALL()`), see the "Selecting Between Overloaded Functions" section on this page; to disambiguate a fake function (the one you place inside `Invoke()`), use a `static_cast` to specify the function's type. For instance, if class `Foo` has methods `char DoThis(int n)` and `bool DoThis(double x) const`, and you want to invoke the latter, you need to write `Invoke(&fake_, static_cast(&FakeFoo::DoThis))` instead of `Invoke(&fake_, &FakeFoo::DoThis)` (The strange-looking thing inside the angled brackets of `static_cast` is the type of a function pointer to the second `DoThis()` method.). * Having to mix a mock and a fake is often a sign of something gone wrong. Perhaps you haven't got used to the interaction-based way of testing yet. Or perhaps your interface is taking on too many roles and should be split up. Therefore, **don't abuse this**. We would only recommend to do it as an intermediate step when you are refactoring your code. Regarding the tip on mixing a mock and a fake, here's an example on why it may be a bad sign: Suppose you have a class `System` for low-level system operations. In particular, it does file and I/O operations. And suppose you want to test how your code uses `System` to do I/O, and you just want the file operations to work normally. If you mock out the entire `System` class, you'll have to provide a fake implementation for the file operation part, which suggests that `System` is taking on too many roles. Instead, you can define a `FileOps` interface and an `IOOps` interface and split `System`'s functionalities into the two. Then you can mock `IOOps` without mocking `FileOps`. ## Delegating Calls to a Real Object ## When using testing doubles (mocks, fakes, stubs, and etc), sometimes their behaviors will differ from those of the real objects. This difference could be either intentional (as in simulating an error such that you can test the error handling code) or unintentional. If your mocks have different behaviors than the real objects by mistake, you could end up with code that passes the tests but fails in production. You can use the _delegating-to-real_ technique to ensure that your mock has the same behavior as the real object while retaining the ability to validate calls. This technique is very similar to the delegating-to-fake technique, the difference being that we use a real object instead of a fake. Here's an example: ```cpp using ::testing::_; using ::testing::AtLeast; using ::testing::Invoke; class MockFoo : public Foo { public: MockFoo() { // By default, all calls are delegated to the real object. ON_CALL(*this, DoThis()) .WillByDefault(Invoke(&real_, &Foo::DoThis)); ON_CALL(*this, DoThat(_)) .WillByDefault(Invoke(&real_, &Foo::DoThat)); ... } MOCK_METHOD0(DoThis, ...); MOCK_METHOD1(DoThat, ...); ... private: Foo real_; }; ... MockFoo mock; EXPECT_CALL(mock, DoThis()) .Times(3); EXPECT_CALL(mock, DoThat("Hi")) .Times(AtLeast(1)); ... use mock in test ... ``` With this, Google Mock will verify that your code made the right calls (with the right arguments, in the right order, called the right number of times, etc), and a real object will answer the calls (so the behavior will be the same as in production). This gives you the best of both worlds. ## Delegating Calls to a Parent Class ## Ideally, you should code to interfaces, whose methods are all pure virtual. In reality, sometimes you do need to mock a virtual method that is not pure (i.e, it already has an implementation). For example: ```cpp class Foo { public: virtual ~Foo(); virtual void Pure(int n) = 0; virtual int Concrete(const char* str) { ... } }; class MockFoo : public Foo { public: // Mocking a pure method. MOCK_METHOD1(Pure, void(int n)); // Mocking a concrete method. Foo::Concrete() is shadowed. MOCK_METHOD1(Concrete, int(const char* str)); }; ``` Sometimes you may want to call `Foo::Concrete()` instead of `MockFoo::Concrete()`. Perhaps you want to do it as part of a stub action, or perhaps your test doesn't need to mock `Concrete()` at all (but it would be oh-so painful to have to define a new mock class whenever you don't need to mock one of its methods). The trick is to leave a back door in your mock class for accessing the real methods in the base class: ```cpp class MockFoo : public Foo { public: // Mocking a pure method. MOCK_METHOD1(Pure, void(int n)); // Mocking a concrete method. Foo::Concrete() is shadowed. MOCK_METHOD1(Concrete, int(const char* str)); // Use this to call Concrete() defined in Foo. int FooConcrete(const char* str) { return Foo::Concrete(str); } }; ``` Now, you can call `Foo::Concrete()` inside an action by: ```cpp using ::testing::_; using ::testing::Invoke; ... EXPECT_CALL(foo, Concrete(_)) .WillOnce(Invoke(&foo, &MockFoo::FooConcrete)); ``` or tell the mock object that you don't want to mock `Concrete()`: ```cpp using ::testing::Invoke; ... ON_CALL(foo, Concrete(_)) .WillByDefault(Invoke(&foo, &MockFoo::FooConcrete)); ``` (Why don't we just write `Invoke(&foo, &Foo::Concrete)`? If you do that, `MockFoo::Concrete()` will be called (and cause an infinite recursion) since `Foo::Concrete()` is virtual. That's just how C++ works.) # Using Matchers # ## Matching Argument Values Exactly ## You can specify exactly which arguments a mock method is expecting: ```cpp using ::testing::Return; ... EXPECT_CALL(foo, DoThis(5)) .WillOnce(Return('a')); EXPECT_CALL(foo, DoThat("Hello", bar)); ``` ## Using Simple Matchers ## You can use matchers to match arguments that have a certain property: ```cpp using ::testing::Ge; using ::testing::NotNull; using ::testing::Return; ... EXPECT_CALL(foo, DoThis(Ge(5))) // The argument must be >= 5. .WillOnce(Return('a')); EXPECT_CALL(foo, DoThat("Hello", NotNull())); // The second argument must not be NULL. ``` A frequently used matcher is `_`, which matches anything: ```cpp using ::testing::_; using ::testing::NotNull; ... EXPECT_CALL(foo, DoThat(_, NotNull())); ``` ## Combining Matchers ## You can build complex matchers from existing ones using `AllOf()`, `AnyOf()`, and `Not()`: ```cpp using ::testing::AllOf; using ::testing::Gt; using ::testing::HasSubstr; using ::testing::Ne; using ::testing::Not; ... // The argument must be > 5 and != 10. EXPECT_CALL(foo, DoThis(AllOf(Gt(5), Ne(10)))); // The first argument must not contain sub-string "blah". EXPECT_CALL(foo, DoThat(Not(HasSubstr("blah")), NULL)); ``` ## Casting Matchers ## Google Mock matchers are statically typed, meaning that the compiler can catch your mistake if you use a matcher of the wrong type (for example, if you use `Eq(5)` to match a `string` argument). Good for you! Sometimes, however, you know what you're doing and want the compiler to give you some slack. One example is that you have a matcher for `long` and the argument you want to match is `int`. While the two types aren't exactly the same, there is nothing really wrong with using a `Matcher` to match an `int` - after all, we can first convert the `int` argument to a `long` before giving it to the matcher. To support this need, Google Mock gives you the `SafeMatcherCast(m)` function. It casts a matcher `m` to type `Matcher`. To ensure safety, Google Mock checks that (let `U` be the type `m` accepts): 1. Type `T` can be implicitly cast to type `U`; 1. When both `T` and `U` are built-in arithmetic types (`bool`, integers, and floating-point numbers), the conversion from `T` to `U` is not lossy (in other words, any value representable by `T` can also be represented by `U`); and 1. When `U` is a reference, `T` must also be a reference (as the underlying matcher may be interested in the address of the `U` value). The code won't compile if any of these conditions aren't met. Here's one example: ```cpp using ::testing::SafeMatcherCast; // A base class and a child class. class Base { ... }; class Derived : public Base { ... }; class MockFoo : public Foo { public: MOCK_METHOD1(DoThis, void(Derived* derived)); }; ... MockFoo foo; // m is a Matcher we got from somewhere. EXPECT_CALL(foo, DoThis(SafeMatcherCast(m))); ``` If you find `SafeMatcherCast(m)` too limiting, you can use a similar function `MatcherCast(m)`. The difference is that `MatcherCast` works as long as you can `static_cast` type `T` to type `U`. `MatcherCast` essentially lets you bypass C++'s type system (`static_cast` isn't always safe as it could throw away information, for example), so be careful not to misuse/abuse it. ## Selecting Between Overloaded Functions ## If you expect an overloaded function to be called, the compiler may need some help on which overloaded version it is. To disambiguate functions overloaded on the const-ness of this object, use the `Const()` argument wrapper. ```cpp using ::testing::ReturnRef; class MockFoo : public Foo { ... MOCK_METHOD0(GetBar, Bar&()); MOCK_CONST_METHOD0(GetBar, const Bar&()); }; ... MockFoo foo; Bar bar1, bar2; EXPECT_CALL(foo, GetBar()) // The non-const GetBar(). .WillOnce(ReturnRef(bar1)); EXPECT_CALL(Const(foo), GetBar()) // The const GetBar(). .WillOnce(ReturnRef(bar2)); ``` (`Const()` is defined by Google Mock and returns a `const` reference to its argument.) To disambiguate overloaded functions with the same number of arguments but different argument types, you may need to specify the exact type of a matcher, either by wrapping your matcher in `Matcher()`, or using a matcher whose type is fixed (`TypedEq`, `An()`, etc): ```cpp using ::testing::An; using ::testing::Lt; using ::testing::Matcher; using ::testing::TypedEq; class MockPrinter : public Printer { public: MOCK_METHOD1(Print, void(int n)); MOCK_METHOD1(Print, void(char c)); }; TEST(PrinterTest, Print) { MockPrinter printer; EXPECT_CALL(printer, Print(An())); // void Print(int); EXPECT_CALL(printer, Print(Matcher(Lt(5)))); // void Print(int); EXPECT_CALL(printer, Print(TypedEq('a'))); // void Print(char); printer.Print(3); printer.Print(6); printer.Print('a'); } ``` ## Performing Different Actions Based on the Arguments ## When a mock method is called, the _last_ matching expectation that's still active will be selected (think "newer overrides older"). So, you can make a method do different things depending on its argument values like this: ```cpp using ::testing::_; using ::testing::Lt; using ::testing::Return; ... // The default case. EXPECT_CALL(foo, DoThis(_)) .WillRepeatedly(Return('b')); // The more specific case. EXPECT_CALL(foo, DoThis(Lt(5))) .WillRepeatedly(Return('a')); ``` Now, if `foo.DoThis()` is called with a value less than 5, `'a'` will be returned; otherwise `'b'` will be returned. ## Matching Multiple Arguments as a Whole ## Sometimes it's not enough to match the arguments individually. For example, we may want to say that the first argument must be less than the second argument. The `With()` clause allows us to match all arguments of a mock function as a whole. For example, ```cpp using ::testing::_; using ::testing::Lt; using ::testing::Ne; ... EXPECT_CALL(foo, InRange(Ne(0), _)) .With(Lt()); ``` says that the first argument of `InRange()` must not be 0, and must be less than the second argument. The expression inside `With()` must be a matcher of type `Matcher< ::testing::tuple >`, where `A1`, ..., `An` are the types of the function arguments. You can also write `AllArgs(m)` instead of `m` inside `.With()`. The two forms are equivalent, but `.With(AllArgs(Lt()))` is more readable than `.With(Lt())`. You can use `Args(m)` to match the `n` selected arguments (as a tuple) against `m`. For example, ```cpp using ::testing::_; using ::testing::AllOf; using ::testing::Args; using ::testing::Lt; ... EXPECT_CALL(foo, Blah(_, _, _)) .With(AllOf(Args<0, 1>(Lt()), Args<1, 2>(Lt()))); ``` says that `Blah()` will be called with arguments `x`, `y`, and `z` where `x < y < z`. As a convenience and example, Google Mock provides some matchers for -2-tuples, including the `Lt()` matcher above. See the [CheatSheet](CheatSheet.md) for +2-tuples, including the `Lt()` matcher above. See the [CheatSheet](cheat_sheet.md) for the complete list. Note that if you want to pass the arguments to a predicate of your own (e.g. `.With(Args<0, 1>(Truly(&MyPredicate)))`), that predicate MUST be written to take a `::testing::tuple` as its argument; Google Mock will pass the `n` selected arguments as _one_ single tuple to the predicate. ## Using Matchers as Predicates ## Have you noticed that a matcher is just a fancy predicate that also knows how to describe itself? Many existing algorithms take predicates as arguments (e.g. those defined in STL's `` header), and it would be a shame if Google Mock matchers are not allowed to participate. Luckily, you can use a matcher where a unary predicate functor is expected by wrapping it inside the `Matches()` function. For example, ```cpp #include #include std::vector v; ... // How many elements in v are >= 10? const int count = count_if(v.begin(), v.end(), Matches(Ge(10))); ``` Since you can build complex matchers from simpler ones easily using Google Mock, this gives you a way to conveniently construct composite predicates (doing the same using STL's `` header is just painful). For example, here's a predicate that's satisfied by any number that is >= 0, <= 100, and != 50: ```cpp Matches(AllOf(Ge(0), Le(100), Ne(50))) ``` ## Using Matchers in Google Test Assertions ## Since matchers are basically predicates that also know how to describe themselves, there is a way to take advantage of them in [Google Test](../../googletest/) assertions. It's called `ASSERT_THAT` and `EXPECT_THAT`: ```cpp ASSERT_THAT(value, matcher); // Asserts that value matches matcher. EXPECT_THAT(value, matcher); // The non-fatal version. ``` For example, in a Google Test test you can write: ```cpp #include "gmock/gmock.h" using ::testing::AllOf; using ::testing::Ge; using ::testing::Le; using ::testing::MatchesRegex; using ::testing::StartsWith; ... EXPECT_THAT(Foo(), StartsWith("Hello")); EXPECT_THAT(Bar(), MatchesRegex("Line \\d+")); ASSERT_THAT(Baz(), AllOf(Ge(5), Le(10))); ``` which (as you can probably guess) executes `Foo()`, `Bar()`, and `Baz()`, and verifies that: * `Foo()` returns a string that starts with `"Hello"`. * `Bar()` returns a string that matches regular expression `"Line \\d+"`. * `Baz()` returns a number in the range [5, 10]. The nice thing about these macros is that _they read like English_. They generate informative messages too. For example, if the first `EXPECT_THAT()` above fails, the message will be something like: ``` Value of: Foo() Actual: "Hi, world!" Expected: starts with "Hello" ``` **Credit:** The idea of `(ASSERT|EXPECT)_THAT` was stolen from the [Hamcrest](https://github.com/hamcrest/) project, which adds `assertThat()` to JUnit. ## Using Predicates as Matchers ## Google Mock provides a built-in set of matchers. In case you find them lacking, you can use an arbitray unary predicate function or functor as a matcher - as long as the predicate accepts a value of the type you want. You do this by wrapping the predicate inside the `Truly()` function, for example: ```cpp using ::testing::Truly; int IsEven(int n) { return (n % 2) == 0 ? 1 : 0; } ... // Bar() must be called with an even number. EXPECT_CALL(foo, Bar(Truly(IsEven))); ``` Note that the predicate function / functor doesn't have to return `bool`. It works as long as the return value can be used as the condition in statement `if (condition) ...`. ## Matching Arguments that Are Not Copyable ## When you do an `EXPECT_CALL(mock_obj, Foo(bar))`, Google Mock saves away a copy of `bar`. When `Foo()` is called later, Google Mock compares the argument to `Foo()` with the saved copy of `bar`. This way, you don't need to worry about `bar` being modified or destroyed after the `EXPECT_CALL()` is executed. The same is true when you use matchers like `Eq(bar)`, `Le(bar)`, and so on. But what if `bar` cannot be copied (i.e. has no copy constructor)? You could define your own matcher function and use it with `Truly()`, as the previous couple of recipes have shown. Or, you may be able to get away from it if you can guarantee that `bar` won't be changed after the `EXPECT_CALL()` is executed. Just tell Google Mock that it should save a reference to `bar`, instead of a copy of it. Here's how: ```cpp using ::testing::Eq; using ::testing::ByRef; using ::testing::Lt; ... // Expects that Foo()'s argument == bar. EXPECT_CALL(mock_obj, Foo(Eq(ByRef(bar)))); // Expects that Foo()'s argument < bar. EXPECT_CALL(mock_obj, Foo(Lt(ByRef(bar)))); ``` Remember: if you do this, don't change `bar` after the `EXPECT_CALL()`, or the result is undefined. ## Validating a Member of an Object ## Often a mock function takes a reference to object as an argument. When matching the argument, you may not want to compare the entire object against a fixed object, as that may be over-specification. Instead, you may need to validate a certain member variable or the result of a certain getter method of the object. You can do this with `Field()` and `Property()`. More specifically, ```cpp Field(&Foo::bar, m) ``` is a matcher that matches a `Foo` object whose `bar` member variable satisfies matcher `m`. ```cpp Property(&Foo::baz, m) ``` is a matcher that matches a `Foo` object whose `baz()` method returns a value that satisfies matcher `m`. For example: | Expression | Description | |:-----------------------------|:-----------------------------------| | `Field(&Foo::number, Ge(3))` | Matches `x` where `x.number >= 3`. | | `Property(&Foo::name, StartsWith("John "))` | Matches `x` where `x.name()` starts with `"John "`. | Note that in `Property(&Foo::baz, ...)`, method `baz()` must take no argument and be declared as `const`. BTW, `Field()` and `Property()` can also match plain pointers to objects. For instance, ```cpp Field(&Foo::number, Ge(3)) ``` matches a plain pointer `p` where `p->number >= 3`. If `p` is `NULL`, the match will always fail regardless of the inner matcher. What if you want to validate more than one members at the same time? Remember that there is `AllOf()`. ## Validating the Value Pointed to by a Pointer Argument ## C++ functions often take pointers as arguments. You can use matchers like `IsNull()`, `NotNull()`, and other comparison matchers to match a pointer, but what if you want to make sure the value _pointed to_ by the pointer, instead of the pointer itself, has a certain property? Well, you can use the `Pointee(m)` matcher. `Pointee(m)` matches a pointer iff `m` matches the value the pointer points to. For example: ```cpp using ::testing::Ge; using ::testing::Pointee; ... EXPECT_CALL(foo, Bar(Pointee(Ge(3)))); ``` expects `foo.Bar()` to be called with a pointer that points to a value greater than or equal to 3. One nice thing about `Pointee()` is that it treats a `NULL` pointer as a match failure, so you can write `Pointee(m)` instead of ```cpp AllOf(NotNull(), Pointee(m)) ``` without worrying that a `NULL` pointer will crash your test. Also, did we tell you that `Pointee()` works with both raw pointers **and** smart pointers (`linked_ptr`, `shared_ptr`, `scoped_ptr`, and etc)? What if you have a pointer to pointer? You guessed it - you can use nested `Pointee()` to probe deeper inside the value. For example, `Pointee(Pointee(Lt(3)))` matches a pointer that points to a pointer that points to a number less than 3 (what a mouthful...). ## Testing a Certain Property of an Object ## Sometimes you want to specify that an object argument has a certain property, but there is no existing matcher that does this. If you want good error messages, you should define a matcher. If you want to do it quick and dirty, you could get away with writing an ordinary function. Let's say you have a mock function that takes an object of type `Foo`, which has an `int bar()` method and an `int baz()` method, and you want to constrain that the argument's `bar()` value plus its `baz()` value is a given number. Here's how you can define a matcher to do it: ```cpp using ::testing::MatcherInterface; using ::testing::MatchResultListener; class BarPlusBazEqMatcher : public MatcherInterface { public: explicit BarPlusBazEqMatcher(int expected_sum) : expected_sum_(expected_sum) {} virtual bool MatchAndExplain(const Foo& foo, MatchResultListener* listener) const { return (foo.bar() + foo.baz()) == expected_sum_; } virtual void DescribeTo(::std::ostream* os) const { *os << "bar() + baz() equals " << expected_sum_; } virtual void DescribeNegationTo(::std::ostream* os) const { *os << "bar() + baz() does not equal " << expected_sum_; } private: const int expected_sum_; }; inline Matcher BarPlusBazEq(int expected_sum) { return MakeMatcher(new BarPlusBazEqMatcher(expected_sum)); } ... EXPECT_CALL(..., DoThis(BarPlusBazEq(5)))...; ``` ## Matching Containers ## Sometimes an STL container (e.g. list, vector, map, ...) is passed to a mock function and you may want to validate it. Since most STL containers support the `==` operator, you can write `Eq(expected_container)` or simply `expected_container` to match a container exactly. Sometimes, though, you may want to be more flexible (for example, the first element must be an exact match, but the second element can be any positive number, and so on). Also, containers used in tests often have a small number of elements, and having to define the expected container out-of-line is a bit of a hassle. You can use the `ElementsAre()` or `UnorderedElementsAre()` matcher in such cases: ```cpp using ::testing::_; using ::testing::ElementsAre; using ::testing::Gt; ... MOCK_METHOD1(Foo, void(const vector& numbers)); ... EXPECT_CALL(mock, Foo(ElementsAre(1, Gt(0), _, 5))); ``` The above matcher says that the container must have 4 elements, which must be 1, greater than 0, anything, and 5 respectively. If you instead write: ```cpp using ::testing::_; using ::testing::Gt; using ::testing::UnorderedElementsAre; ... MOCK_METHOD1(Foo, void(const vector& numbers)); ... EXPECT_CALL(mock, Foo(UnorderedElementsAre(1, Gt(0), _, 5))); ``` It means that the container must have 4 elements, which under some permutation must be 1, greater than 0, anything, and 5 respectively. `ElementsAre()` and `UnorderedElementsAre()` are overloaded to take 0 to 10 arguments. If more are needed, you can place them in a C-style array and use `ElementsAreArray()` or `UnorderedElementsAreArray()` instead: ```cpp using ::testing::ElementsAreArray; ... // ElementsAreArray accepts an array of element values. const int expected_vector1[] = { 1, 5, 2, 4, ... }; EXPECT_CALL(mock, Foo(ElementsAreArray(expected_vector1))); // Or, an array of element matchers. Matcher expected_vector2 = { 1, Gt(2), _, 3, ... }; EXPECT_CALL(mock, Foo(ElementsAreArray(expected_vector2))); ``` In case the array needs to be dynamically created (and therefore the array size cannot be inferred by the compiler), you can give `ElementsAreArray()` an additional argument to specify the array size: ```cpp using ::testing::ElementsAreArray; ... int* const expected_vector3 = new int[count]; ... fill expected_vector3 with values ... EXPECT_CALL(mock, Foo(ElementsAreArray(expected_vector3, count))); ``` **Tips:** * `ElementsAre*()` can be used to match _any_ container that implements the STL iterator pattern (i.e. it has a `const_iterator` type and supports `begin()/end()`), not just the ones defined in STL. It will even work with container types yet to be written - as long as they follows the above pattern. * You can use nested `ElementsAre*()` to match nested (multi-dimensional) containers. * If the container is passed by pointer instead of by reference, just write `Pointee(ElementsAre*(...))`. * The order of elements _matters_ for `ElementsAre*()`. Therefore don't use it with containers whose element order is undefined (e.g. `hash_map`). ## Sharing Matchers ## Under the hood, a Google Mock matcher object consists of a pointer to a ref-counted implementation object. Copying matchers is allowed and very efficient, as only the pointer is copied. When the last matcher that references the implementation object dies, the implementation object will be deleted. Therefore, if you have some complex matcher that you want to use again and again, there is no need to build it every time. Just assign it to a matcher variable and use that variable repeatedly! For example, ```cpp Matcher in_range = AllOf(Gt(5), Le(10)); ... use in_range as a matcher in multiple EXPECT_CALLs ... ``` # Setting Expectations # ## Knowing When to Expect ## `ON_CALL` is likely the single most under-utilized construct in Google Mock. There are basically two constructs for defining the behavior of a mock object: `ON_CALL` and `EXPECT_CALL`. The difference? `ON_CALL` defines what happens when a mock method is called, but _doesn't imply any expectation on the method being called._ `EXPECT_CALL` not only defines the behavior, but also sets an expectation that _the method will be called with the given arguments, for the given number of times_ (and _in the given order_ when you specify the order too). Since `EXPECT_CALL` does more, isn't it better than `ON_CALL`? Not really. Every `EXPECT_CALL` adds a constraint on the behavior of the code under test. Having more constraints than necessary is _baaad_ - even worse than not having enough constraints. This may be counter-intuitive. How could tests that verify more be worse than tests that verify less? Isn't verification the whole point of tests? The answer, lies in _what_ a test should verify. **A good test verifies the contract of the code.** If a test over-specifies, it doesn't leave enough freedom to the implementation. As a result, changing the implementation without breaking the contract (e.g. refactoring and optimization), which should be perfectly fine to do, can break such tests. Then you have to spend time fixing them, only to see them broken again the next time the implementation is changed. Keep in mind that one doesn't have to verify more than one property in one test. In fact, **it's a good style to verify only one thing in one test.** If you do that, a bug will likely break only one or two tests instead of dozens (which case would you rather debug?). If you are also in the habit of giving tests descriptive names that tell what they verify, you can often easily guess what's wrong just from the test log itself. So use `ON_CALL` by default, and only use `EXPECT_CALL` when you actually intend to verify that the call is made. For example, you may have a bunch of `ON_CALL`s in your test fixture to set the common mock behavior shared by all tests in the same group, and write (scarcely) different `EXPECT_CALL`s in different `TEST_F`s to verify different aspects of the code's behavior. Compared with the style where each `TEST` has many `EXPECT_CALL`s, this leads to tests that are more resilient to implementational changes (and thus less likely to require maintenance) and makes the intent of the tests more obvious (so they are easier to maintain when you do need to maintain them). If you are bothered by the "Uninteresting mock function call" message printed when a mock method without an `EXPECT_CALL` is called, you may use a `NiceMock` instead to suppress all such messages for the mock object, or suppress the message for specific methods by adding `EXPECT_CALL(...).Times(AnyNumber())`. DO NOT suppress it by blindly adding an `EXPECT_CALL(...)`, or you'll have a test that's a pain to maintain. ## Ignoring Uninteresting Calls ## If you are not interested in how a mock method is called, just don't say anything about it. In this case, if the method is ever called, Google Mock will perform its default action to allow the test program to continue. If you are not happy with the default action taken by Google Mock, you can override it using `DefaultValue::Set()` (described later in this document) or `ON_CALL()`. Please note that once you expressed interest in a particular mock method (via `EXPECT_CALL()`), all invocations to it must match some expectation. If this function is called but the arguments don't match any `EXPECT_CALL()` statement, it will be an error. ## Disallowing Unexpected Calls ## If a mock method shouldn't be called at all, explicitly say so: ```cpp using ::testing::_; ... EXPECT_CALL(foo, Bar(_)) .Times(0); ``` If some calls to the method are allowed, but the rest are not, just list all the expected calls: ```cpp using ::testing::AnyNumber; using ::testing::Gt; ... EXPECT_CALL(foo, Bar(5)); EXPECT_CALL(foo, Bar(Gt(10))) .Times(AnyNumber()); ``` A call to `foo.Bar()` that doesn't match any of the `EXPECT_CALL()` statements will be an error. ## Understanding Uninteresting vs Unexpected Calls ## _Uninteresting_ calls and _unexpected_ calls are different concepts in Google Mock. _Very_ different. A call `x.Y(...)` is **uninteresting** if there's _not even a single_ `EXPECT_CALL(x, Y(...))` set. In other words, the test isn't interested in the `x.Y()` method at all, as evident in that the test doesn't care to say anything about it. A call `x.Y(...)` is **unexpected** if there are some `EXPECT_CALL(x, Y(...))s` set, but none of them matches the call. Put another way, the test is interested in the `x.Y()` method (therefore it _explicitly_ sets some `EXPECT_CALL` to verify how it's called); however, the verification fails as the test doesn't expect this particular call to happen. **An unexpected call is always an error,** as the code under test doesn't behave the way the test expects it to behave. **By default, an uninteresting call is not an error,** as it violates no constraint specified by the test. (Google Mock's philosophy is that saying nothing means there is no constraint.) However, it leads to a warning, as it _might_ indicate a problem (e.g. the test author might have forgotten to specify a constraint). In Google Mock, `NiceMock` and `StrictMock` can be used to make a mock class "nice" or "strict". How does this affect uninteresting calls and unexpected calls? A **nice mock** suppresses uninteresting call warnings. It is less chatty than the default mock, but otherwise is the same. If a test fails with a default mock, it will also fail using a nice mock instead. And vice versa. Don't expect making a mock nice to change the test's result. A **strict mock** turns uninteresting call warnings into errors. So making a mock strict may change the test's result. Let's look at an example: ```cpp TEST(...) { NiceMock mock_registry; EXPECT_CALL(mock_registry, GetDomainOwner("google.com")) .WillRepeatedly(Return("Larry Page")); // Use mock_registry in code under test. ... &mock_registry ... } ``` The sole `EXPECT_CALL` here says that all calls to `GetDomainOwner()` must have `"google.com"` as the argument. If `GetDomainOwner("yahoo.com")` is called, it will be an unexpected call, and thus an error. Having a nice mock doesn't change the severity of an unexpected call. So how do we tell Google Mock that `GetDomainOwner()` can be called with some other arguments as well? The standard technique is to add a "catch all" `EXPECT_CALL`: ```cpp EXPECT_CALL(mock_registry, GetDomainOwner(_)) .Times(AnyNumber()); // catches all other calls to this method. EXPECT_CALL(mock_registry, GetDomainOwner("google.com")) .WillRepeatedly(Return("Larry Page")); ``` Remember that `_` is the wildcard matcher that matches anything. With this, if `GetDomainOwner("google.com")` is called, it will do what the second `EXPECT_CALL` says; if it is called with a different argument, it will do what the first `EXPECT_CALL` says. Note that the order of the two `EXPECT_CALLs` is important, as a newer `EXPECT_CALL` takes precedence over an older one. For more on uninteresting calls, nice mocks, and strict mocks, read ["The Nice, the Strict, and the Naggy"](#the-nice-the-strict-and-the-naggy). ## Expecting Ordered Calls ## Although an `EXPECT_CALL()` statement defined earlier takes precedence when Google Mock tries to match a function call with an expectation, by default calls don't have to happen in the order `EXPECT_CALL()` statements are written. For example, if the arguments match the matchers in the third `EXPECT_CALL()`, but not those in the first two, then the third expectation will be used. If you would rather have all calls occur in the order of the expectations, put the `EXPECT_CALL()` statements in a block where you define a variable of type `InSequence`: ```cpp using ::testing::_; using ::testing::InSequence; { InSequence s; EXPECT_CALL(foo, DoThis(5)); EXPECT_CALL(bar, DoThat(_)) .Times(2); EXPECT_CALL(foo, DoThis(6)); } ``` In this example, we expect a call to `foo.DoThis(5)`, followed by two calls to `bar.DoThat()` where the argument can be anything, which are in turn followed by a call to `foo.DoThis(6)`. If a call occurred out-of-order, Google Mock will report an error. ## Expecting Partially Ordered Calls ## Sometimes requiring everything to occur in a predetermined order can lead to brittle tests. For example, we may care about `A` occurring before both `B` and `C`, but aren't interested in the relative order of `B` and `C`. In this case, the test should reflect our real intent, instead of being overly constraining. Google Mock allows you to impose an arbitrary DAG (directed acyclic graph) on the calls. One way to express the DAG is to use the -[After](CheatSheet.md#the-after-clause) clause of `EXPECT_CALL`. +[After](cheat_sheet.md#the-after-clause) clause of `EXPECT_CALL`. Another way is via the `InSequence()` clause (not the same as the `InSequence` class), which we borrowed from jMock 2. It's less flexible than `After()`, but more convenient when you have long chains of sequential calls, as it doesn't require you to come up with different names for the expectations in the chains. Here's how it works: If we view `EXPECT_CALL()` statements as nodes in a graph, and add an edge from node A to node B wherever A must occur before B, we can get a DAG. We use the term "sequence" to mean a directed path in this DAG. Now, if we decompose the DAG into sequences, we just need to know which sequences each `EXPECT_CALL()` belongs to in order to be able to reconstruct the original DAG. So, to specify the partial order on the expectations we need to do two things: first to define some `Sequence` objects, and then for each `EXPECT_CALL()` say which `Sequence` objects it is part of. Expectations in the same sequence must occur in the order they are written. For example, ```cpp using ::testing::Sequence; Sequence s1, s2; EXPECT_CALL(foo, A()) .InSequence(s1, s2); EXPECT_CALL(bar, B()) .InSequence(s1); EXPECT_CALL(bar, C()) .InSequence(s2); EXPECT_CALL(foo, D()) .InSequence(s2); ``` specifies the following DAG (where `s1` is `A -> B`, and `s2` is `A -> C -> D`): ``` +---> B | A ---| | +---> C ---> D ``` This means that A must occur before B and C, and C must occur before D. There's no restriction about the order other than these. ## Controlling When an Expectation Retires ## When a mock method is called, Google Mock only consider expectations that are still active. An expectation is active when created, and becomes inactive (aka _retires_) when a call that has to occur later has occurred. For example, in ```cpp using ::testing::_; using ::testing::Sequence; Sequence s1, s2; EXPECT_CALL(log, Log(WARNING, _, "File too large.")) // #1 .Times(AnyNumber()) .InSequence(s1, s2); EXPECT_CALL(log, Log(WARNING, _, "Data set is empty.")) // #2 .InSequence(s1); EXPECT_CALL(log, Log(WARNING, _, "User not found.")) // #3 .InSequence(s2); ``` as soon as either #2 or #3 is matched, #1 will retire. If a warning `"File too large."` is logged after this, it will be an error. Note that an expectation doesn't retire automatically when it's saturated. For example, ```cpp using ::testing::_; ... EXPECT_CALL(log, Log(WARNING, _, _)); // #1 EXPECT_CALL(log, Log(WARNING, _, "File too large.")); // #2 ``` says that there will be exactly one warning with the message `"File too large."`. If the second warning contains this message too, #2 will match again and result in an upper-bound-violated error. If this is not what you want, you can ask an expectation to retire as soon as it becomes saturated: ```cpp using ::testing::_; ... EXPECT_CALL(log, Log(WARNING, _, _)); // #1 EXPECT_CALL(log, Log(WARNING, _, "File too large.")) // #2 .RetiresOnSaturation(); ``` Here #2 can be used only once, so if you have two warnings with the message `"File too large."`, the first will match #2 and the second will match #1 - there will be no error. # Using Actions # ## Returning References from Mock Methods ## If a mock function's return type is a reference, you need to use `ReturnRef()` instead of `Return()` to return a result: ```cpp using ::testing::ReturnRef; class MockFoo : public Foo { public: MOCK_METHOD0(GetBar, Bar&()); }; ... MockFoo foo; Bar bar; EXPECT_CALL(foo, GetBar()) .WillOnce(ReturnRef(bar)); ``` ## Returning Live Values from Mock Methods ## The `Return(x)` action saves a copy of `x` when the action is _created_, and always returns the same value whenever it's executed. Sometimes you may want to instead return the _live_ value of `x` (i.e. its value at the time when the action is _executed_.). If the mock function's return type is a reference, you can do it using `ReturnRef(x)`, as shown in the previous recipe ("Returning References from Mock Methods"). However, Google Mock doesn't let you use `ReturnRef()` in a mock function whose return type is not a reference, as doing that usually indicates a user error. So, what shall you do? You may be tempted to try `ByRef()`: ```cpp using testing::ByRef; using testing::Return; class MockFoo : public Foo { public: MOCK_METHOD0(GetValue, int()); }; ... int x = 0; MockFoo foo; EXPECT_CALL(foo, GetValue()) .WillRepeatedly(Return(ByRef(x))); x = 42; EXPECT_EQ(42, foo.GetValue()); ``` Unfortunately, it doesn't work here. The above code will fail with error: ``` Value of: foo.GetValue() Actual: 0 Expected: 42 ``` The reason is that `Return(value)` converts `value` to the actual return type of the mock function at the time when the action is _created_, not when it is _executed_. (This behavior was chosen for the action to be safe when `value` is a proxy object that references some temporary objects.) As a result, `ByRef(x)` is converted to an `int` value (instead of a `const int&`) when the expectation is set, and `Return(ByRef(x))` will always return 0. `ReturnPointee(pointer)` was provided to solve this problem specifically. It returns the value pointed to by `pointer` at the time the action is _executed_: ```cpp using testing::ReturnPointee; ... int x = 0; MockFoo foo; EXPECT_CALL(foo, GetValue()) .WillRepeatedly(ReturnPointee(&x)); // Note the & here. x = 42; EXPECT_EQ(42, foo.GetValue()); // This will succeed now. ``` ## Combining Actions ## Want to do more than one thing when a function is called? That's fine. `DoAll()` allow you to do sequence of actions every time. Only the return value of the last action in the sequence will be used. ```cpp using ::testing::DoAll; class MockFoo : public Foo { public: MOCK_METHOD1(Bar, bool(int n)); }; ... EXPECT_CALL(foo, Bar(_)) .WillOnce(DoAll(action_1, action_2, ... action_n)); ``` ## Mocking Side Effects ## Sometimes a method exhibits its effect not via returning a value but via side effects. For example, it may change some global state or modify an output argument. To mock side effects, in general you can define your own action by implementing `::testing::ActionInterface`. If all you need to do is to change an output argument, the built-in `SetArgPointee()` action is convenient: ```cpp using ::testing::SetArgPointee; class MockMutator : public Mutator { public: MOCK_METHOD2(Mutate, void(bool mutate, int* value)); ... }; ... MockMutator mutator; EXPECT_CALL(mutator, Mutate(true, _)) .WillOnce(SetArgPointee<1>(5)); ``` In this example, when `mutator.Mutate()` is called, we will assign 5 to the `int` variable pointed to by argument #1 (0-based). `SetArgPointee()` conveniently makes an internal copy of the value you pass to it, removing the need to keep the value in scope and alive. The implication however is that the value must have a copy constructor and assignment operator. If the mock method also needs to return a value as well, you can chain `SetArgPointee()` with `Return()` using `DoAll()`: ```cpp using ::testing::_; using ::testing::Return; using ::testing::SetArgPointee; class MockMutator : public Mutator { public: ... MOCK_METHOD1(MutateInt, bool(int* value)); }; ... MockMutator mutator; EXPECT_CALL(mutator, MutateInt(_)) .WillOnce(DoAll(SetArgPointee<0>(5), Return(true))); ``` If the output argument is an array, use the `SetArrayArgument(first, last)` action instead. It copies the elements in source range `[first, last)` to the array pointed to by the `N`-th (0-based) argument: ```cpp using ::testing::NotNull; using ::testing::SetArrayArgument; class MockArrayMutator : public ArrayMutator { public: MOCK_METHOD2(Mutate, void(int* values, int num_values)); ... }; ... MockArrayMutator mutator; int values[5] = { 1, 2, 3, 4, 5 }; EXPECT_CALL(mutator, Mutate(NotNull(), 5)) .WillOnce(SetArrayArgument<0>(values, values + 5)); ``` This also works when the argument is an output iterator: ```cpp using ::testing::_; using ::testing::SetArrayArgument; class MockRolodex : public Rolodex { public: MOCK_METHOD1(GetNames, void(std::back_insert_iterator >)); ... }; ... MockRolodex rolodex; vector names; names.push_back("George"); names.push_back("John"); names.push_back("Thomas"); EXPECT_CALL(rolodex, GetNames(_)) .WillOnce(SetArrayArgument<0>(names.begin(), names.end())); ``` ## Changing a Mock Object's Behavior Based on the State ## If you expect a call to change the behavior of a mock object, you can use `::testing::InSequence` to specify different behaviors before and after the call: ```cpp using ::testing::InSequence; using ::testing::Return; ... { InSequence seq; EXPECT_CALL(my_mock, IsDirty()) .WillRepeatedly(Return(true)); EXPECT_CALL(my_mock, Flush()); EXPECT_CALL(my_mock, IsDirty()) .WillRepeatedly(Return(false)); } my_mock.FlushIfDirty(); ``` This makes `my_mock.IsDirty()` return `true` before `my_mock.Flush()` is called and return `false` afterwards. If the behavior change is more complex, you can store the effects in a variable and make a mock method get its return value from that variable: ```cpp using ::testing::_; using ::testing::SaveArg; using ::testing::Return; ACTION_P(ReturnPointee, p) { return *p; } ... int previous_value = 0; EXPECT_CALL(my_mock, GetPrevValue()) .WillRepeatedly(ReturnPointee(&previous_value)); EXPECT_CALL(my_mock, UpdateValue(_)) .WillRepeatedly(SaveArg<0>(&previous_value)); my_mock.DoSomethingToUpdateValue(); ``` Here `my_mock.GetPrevValue()` will always return the argument of the last `UpdateValue()` call. ## Setting the Default Value for a Return Type ## If a mock method's return type is a built-in C++ type or pointer, by default it will return 0 when invoked. Also, in C++ 11 and above, a mock method whose return type has a default constructor will return a default-constructed value by default. You only need to specify an action if this default value doesn't work for you. Sometimes, you may want to change this default value, or you may want to specify a default value for types Google Mock doesn't know about. You can do this using the `::testing::DefaultValue` class template: ```cpp class MockFoo : public Foo { public: MOCK_METHOD0(CalculateBar, Bar()); }; ... Bar default_bar; // Sets the default return value for type Bar. DefaultValue::Set(default_bar); MockFoo foo; // We don't need to specify an action here, as the default // return value works for us. EXPECT_CALL(foo, CalculateBar()); foo.CalculateBar(); // This should return default_bar. // Unsets the default return value. DefaultValue::Clear(); ``` Please note that changing the default value for a type can make you tests hard to understand. We recommend you to use this feature judiciously. For example, you may want to make sure the `Set()` and `Clear()` calls are right next to the code that uses your mock. ## Setting the Default Actions for a Mock Method ## You've learned how to change the default value of a given type. However, this may be too coarse for your purpose: perhaps you have two mock methods with the same return type and you want them to have different behaviors. The `ON_CALL()` macro allows you to customize your mock's behavior at the method level: ```cpp using ::testing::_; using ::testing::AnyNumber; using ::testing::Gt; using ::testing::Return; ... ON_CALL(foo, Sign(_)) .WillByDefault(Return(-1)); ON_CALL(foo, Sign(0)) .WillByDefault(Return(0)); ON_CALL(foo, Sign(Gt(0))) .WillByDefault(Return(1)); EXPECT_CALL(foo, Sign(_)) .Times(AnyNumber()); foo.Sign(5); // This should return 1. foo.Sign(-9); // This should return -1. foo.Sign(0); // This should return 0. ``` As you may have guessed, when there are more than one `ON_CALL()` statements, the news order take precedence over the older ones. In other words, the **last** one that matches the function arguments will be used. This matching order allows you to set up the common behavior in a mock object's constructor or the test fixture's set-up phase and specialize the mock's behavior later. ## Using Functions/Methods/Functors as Actions ## If the built-in actions don't suit you, you can easily use an existing function, method, or functor as an action: ```cpp using ::testing::_; using ::testing::Invoke; class MockFoo : public Foo { public: MOCK_METHOD2(Sum, int(int x, int y)); MOCK_METHOD1(ComplexJob, bool(int x)); }; int CalculateSum(int x, int y) { return x + y; } class Helper { public: bool ComplexJob(int x); }; ... MockFoo foo; Helper helper; EXPECT_CALL(foo, Sum(_, _)) .WillOnce(Invoke(CalculateSum)); EXPECT_CALL(foo, ComplexJob(_)) .WillOnce(Invoke(&helper, &Helper::ComplexJob)); foo.Sum(5, 6); // Invokes CalculateSum(5, 6). foo.ComplexJob(10); // Invokes helper.ComplexJob(10); ``` The only requirement is that the type of the function, etc must be _compatible_ with the signature of the mock function, meaning that the latter's arguments can be implicitly converted to the corresponding arguments of the former, and the former's return type can be implicitly converted to that of the latter. So, you can invoke something whose type is _not_ exactly the same as the mock function, as long as it's safe to do so - nice, huh? ## Invoking a Function/Method/Functor Without Arguments ## `Invoke()` is very useful for doing actions that are more complex. It passes the mock function's arguments to the function or functor being invoked such that the callee has the full context of the call to work with. If the invoked function is not interested in some or all of the arguments, it can simply ignore them. Yet, a common pattern is that a test author wants to invoke a function without the arguments of the mock function. `Invoke()` allows her to do that using a wrapper function that throws away the arguments before invoking an underlining nullary function. Needless to say, this can be tedious and obscures the intent of the test. `InvokeWithoutArgs()` solves this problem. It's like `Invoke()` except that it doesn't pass the mock function's arguments to the callee. Here's an example: ```cpp using ::testing::_; using ::testing::InvokeWithoutArgs; class MockFoo : public Foo { public: MOCK_METHOD1(ComplexJob, bool(int n)); }; bool Job1() { ... } ... MockFoo foo; EXPECT_CALL(foo, ComplexJob(_)) .WillOnce(InvokeWithoutArgs(Job1)); foo.ComplexJob(10); // Invokes Job1(). ``` ## Invoking an Argument of the Mock Function ## Sometimes a mock function will receive a function pointer or a functor (in other words, a "callable") as an argument, e.g. ```cpp class MockFoo : public Foo { public: MOCK_METHOD2(DoThis, bool(int n, bool (*fp)(int))); }; ``` and you may want to invoke this callable argument: ```cpp using ::testing::_; ... MockFoo foo; EXPECT_CALL(foo, DoThis(_, _)) .WillOnce(...); // Will execute (*fp)(5), where fp is the // second argument DoThis() receives. ``` Arghh, you need to refer to a mock function argument but your version of C++ has no lambdas, so you have to define your own action. :-( Or do you really? Well, Google Mock has an action to solve _exactly_ this problem: ```cpp InvokeArgument(arg_1, arg_2, ..., arg_m) ``` will invoke the `N`-th (0-based) argument the mock function receives, with `arg_1`, `arg_2`, ..., and `arg_m`. No matter if the argument is a function pointer or a functor, Google Mock handles them both. With that, you could write: ```cpp using ::testing::_; using ::testing::InvokeArgument; ... EXPECT_CALL(foo, DoThis(_, _)) .WillOnce(InvokeArgument<1>(5)); // Will execute (*fp)(5), where fp is the // second argument DoThis() receives. ``` What if the callable takes an argument by reference? No problem - just wrap it inside `ByRef()`: ```cpp ... MOCK_METHOD1(Bar, bool(bool (*fp)(int, const Helper&))); ... using ::testing::_; using ::testing::ByRef; using ::testing::InvokeArgument; ... MockFoo foo; Helper helper; ... EXPECT_CALL(foo, Bar(_)) .WillOnce(InvokeArgument<0>(5, ByRef(helper))); // ByRef(helper) guarantees that a reference to helper, not a copy of it, // will be passed to the callable. ``` What if the callable takes an argument by reference and we do **not** wrap the argument in `ByRef()`? Then `InvokeArgument()` will _make a copy_ of the argument, and pass a _reference to the copy_, instead of a reference to the original value, to the callable. This is especially handy when the argument is a temporary value: ```cpp ... MOCK_METHOD1(DoThat, bool(bool (*f)(const double& x, const string& s))); ... using ::testing::_; using ::testing::InvokeArgument; ... MockFoo foo; ... EXPECT_CALL(foo, DoThat(_)) .WillOnce(InvokeArgument<0>(5.0, string("Hi"))); // Will execute (*f)(5.0, string("Hi")), where f is the function pointer // DoThat() receives. Note that the values 5.0 and string("Hi") are // temporary and dead once the EXPECT_CALL() statement finishes. Yet // it's fine to perform this action later, since a copy of the values // are kept inside the InvokeArgument action. ``` ## Ignoring an Action's Result ## Sometimes you have an action that returns _something_, but you need an action that returns `void` (perhaps you want to use it in a mock function that returns `void`, or perhaps it needs to be used in `DoAll()` and it's not the last in the list). `IgnoreResult()` lets you do that. For example: ```cpp using ::testing::_; using ::testing::Invoke; using ::testing::Return; int Process(const MyData& data); string DoSomething(); class MockFoo : public Foo { public: MOCK_METHOD1(Abc, void(const MyData& data)); MOCK_METHOD0(Xyz, bool()); }; ... MockFoo foo; EXPECT_CALL(foo, Abc(_)) // .WillOnce(Invoke(Process)); // The above line won't compile as Process() returns int but Abc() needs // to return void. .WillOnce(IgnoreResult(Invoke(Process))); EXPECT_CALL(foo, Xyz()) .WillOnce(DoAll(IgnoreResult(Invoke(DoSomething)), // Ignores the string DoSomething() returns. Return(true))); ``` Note that you **cannot** use `IgnoreResult()` on an action that already returns `void`. Doing so will lead to ugly compiler errors. ## Selecting an Action's Arguments ## Say you have a mock function `Foo()` that takes seven arguments, and you have a custom action that you want to invoke when `Foo()` is called. Trouble is, the custom action only wants three arguments: ```cpp using ::testing::_; using ::testing::Invoke; ... MOCK_METHOD7(Foo, bool(bool visible, const string& name, int x, int y, const map, double>& weight, double min_weight, double max_wight)); ... bool IsVisibleInQuadrant1(bool visible, int x, int y) { return visible && x >= 0 && y >= 0; } ... EXPECT_CALL(mock, Foo(_, _, _, _, _, _, _)) .WillOnce(Invoke(IsVisibleInQuadrant1)); // Uh, won't compile. :-( ``` To please the compiler God, you can to define an "adaptor" that has the same signature as `Foo()` and calls the custom action with the right arguments: ```cpp using ::testing::_; using ::testing::Invoke; bool MyIsVisibleInQuadrant1(bool visible, const string& name, int x, int y, const map, double>& weight, double min_weight, double max_wight) { return IsVisibleInQuadrant1(visible, x, y); } ... EXPECT_CALL(mock, Foo(_, _, _, _, _, _, _)) .WillOnce(Invoke(MyIsVisibleInQuadrant1)); // Now it works. ``` But isn't this awkward? Google Mock provides a generic _action adaptor_, so you can spend your time minding more important business than writing your own adaptors. Here's the syntax: ```cpp WithArgs(action) ``` creates an action that passes the arguments of the mock function at the given indices (0-based) to the inner `action` and performs it. Using `WithArgs`, our original example can be written as: ```cpp using ::testing::_; using ::testing::Invoke; using ::testing::WithArgs; ... EXPECT_CALL(mock, Foo(_, _, _, _, _, _, _)) .WillOnce(WithArgs<0, 2, 3>(Invoke(IsVisibleInQuadrant1))); // No need to define your own adaptor. ``` For better readability, Google Mock also gives you: * `WithoutArgs(action)` when the inner `action` takes _no_ argument, and * `WithArg(action)` (no `s` after `Arg`) when the inner `action` takes _one_ argument. As you may have realized, `InvokeWithoutArgs(...)` is just syntactic sugar for `WithoutArgs(Invoke(...))`. Here are more tips: * The inner action used in `WithArgs` and friends does not have to be `Invoke()` -- it can be anything. * You can repeat an argument in the argument list if necessary, e.g. `WithArgs<2, 3, 3, 5>(...)`. * You can change the order of the arguments, e.g. `WithArgs<3, 2, 1>(...)`. * The types of the selected arguments do _not_ have to match the signature of the inner action exactly. It works as long as they can be implicitly converted to the corresponding arguments of the inner action. For example, if the 4-th argument of the mock function is an `int` and `my_action` takes a `double`, `WithArg<4>(my_action)` will work. ## Ignoring Arguments in Action Functions ## The selecting-an-action's-arguments recipe showed us one way to make a mock function and an action with incompatible argument lists fit together. The downside is that wrapping the action in `WithArgs<...>()` can get tedious for people writing the tests. If you are defining a function, method, or functor to be used with `Invoke*()`, and you are not interested in some of its arguments, an alternative to `WithArgs` is to declare the uninteresting arguments as `Unused`. This makes the definition less cluttered and less fragile in case the types of the uninteresting arguments change. It could also increase the chance the action function can be reused. For example, given ```cpp MOCK_METHOD3(Foo, double(const string& label, double x, double y)); MOCK_METHOD3(Bar, double(int index, double x, double y)); ``` instead of ```cpp using ::testing::_; using ::testing::Invoke; double DistanceToOriginWithLabel(const string& label, double x, double y) { return sqrt(x*x + y*y); } double DistanceToOriginWithIndex(int index, double x, double y) { return sqrt(x*x + y*y); } ... EXEPCT_CALL(mock, Foo("abc", _, _)) .WillOnce(Invoke(DistanceToOriginWithLabel)); EXEPCT_CALL(mock, Bar(5, _, _)) .WillOnce(Invoke(DistanceToOriginWithIndex)); ``` you could write ```cpp using ::testing::_; using ::testing::Invoke; using ::testing::Unused; double DistanceToOrigin(Unused, double x, double y) { return sqrt(x*x + y*y); } ... EXEPCT_CALL(mock, Foo("abc", _, _)) .WillOnce(Invoke(DistanceToOrigin)); EXEPCT_CALL(mock, Bar(5, _, _)) .WillOnce(Invoke(DistanceToOrigin)); ``` ## Sharing Actions ## Just like matchers, a Google Mock action object consists of a pointer to a ref-counted implementation object. Therefore copying actions is also allowed and very efficient. When the last action that references the implementation object dies, the implementation object will be deleted. If you have some complex action that you want to use again and again, you may not have to build it from scratch every time. If the action doesn't have an internal state (i.e. if it always does the same thing no matter how many times it has been called), you can assign it to an action variable and use that variable repeatedly. For example: ```cpp Action set_flag = DoAll(SetArgPointee<0>(5), Return(true)); ... use set_flag in .WillOnce() and .WillRepeatedly() ... ``` However, if the action has its own state, you may be surprised if you share the action object. Suppose you have an action factory `IncrementCounter(init)` which creates an action that increments and returns a counter whose initial value is `init`, using two actions created from the same expression and using a shared action will exihibit different behaviors. Example: ```cpp EXPECT_CALL(foo, DoThis()) .WillRepeatedly(IncrementCounter(0)); EXPECT_CALL(foo, DoThat()) .WillRepeatedly(IncrementCounter(0)); foo.DoThis(); // Returns 1. foo.DoThis(); // Returns 2. foo.DoThat(); // Returns 1 - Blah() uses a different // counter than Bar()'s. ``` versus ```cpp Action increment = IncrementCounter(0); EXPECT_CALL(foo, DoThis()) .WillRepeatedly(increment); EXPECT_CALL(foo, DoThat()) .WillRepeatedly(increment); foo.DoThis(); // Returns 1. foo.DoThis(); // Returns 2. foo.DoThat(); // Returns 3 - the counter is shared. ``` # Misc Recipes on Using Google Mock # ## Mocking Methods That Use Move-Only Types ## C++11 introduced *move-only types*. A move-only-typed value can be moved from one object to another, but cannot be copied. `std::unique_ptr` is probably the most commonly used move-only type. Mocking a method that takes and/or returns move-only types presents some challenges, but nothing insurmountable. This recipe shows you how you can do it. Note that the support for move-only method arguments was only introduced to gMock in April 2017; in older code, you may find more complex [workarounds](#legacy-workarounds-for-move-only-types) for lack of this feature. Let’s say we are working on a fictional project that lets one post and share snippets called “buzzes”. Your code uses these types: ```cpp enum class AccessLevel { kInternal, kPublic }; class Buzz { public: explicit Buzz(AccessLevel access) { ... } ... }; class Buzzer { public: virtual ~Buzzer() {} virtual std::unique_ptr MakeBuzz(StringPiece text) = 0; virtual bool ShareBuzz(std::unique_ptr buzz, int64_t timestamp) = 0; ... }; ``` A `Buzz` object represents a snippet being posted. A class that implements the `Buzzer` interface is capable of creating and sharing `Buzz`es. Methods in `Buzzer` may return a `unique_ptr` or take a `unique_ptr`. Now we need to mock `Buzzer` in our tests. To mock a method that accepts or returns move-only types, you just use the familiar `MOCK_METHOD` syntax as usual: ```cpp class MockBuzzer : public Buzzer { public: MOCK_METHOD1(MakeBuzz, std::unique_ptr(StringPiece text)); MOCK_METHOD2(ShareBuzz, bool(std::unique_ptr buzz, int64_t timestamp)); }; ``` Now that we have the mock class defined, we can use it in tests. In the following code examples, we assume that we have defined a `MockBuzzer` object named `mock_buzzer_`: ```cpp MockBuzzer mock_buzzer_; ``` First let’s see how we can set expectations on the `MakeBuzz()` method, which returns a `unique_ptr`. As usual, if you set an expectation without an action (i.e. the `.WillOnce()` or `.WillRepeated()` clause), when that expectation fires, the default action for that method will be taken. Since `unique_ptr<>` has a default constructor that returns a null `unique_ptr`, that’s what you’ll get if you don’t specify an action: ```cpp // Use the default action. EXPECT_CALL(mock_buzzer_, MakeBuzz("hello")); // Triggers the previous EXPECT_CALL. EXPECT_EQ(nullptr, mock_buzzer_.MakeBuzz("hello")); ``` If you are not happy with the default action, you can tweak it as usual; see [Setting Default Actions](#setting-the-default-actions-for-a-mock-method). If you just need to return a pre-defined move-only value, you can use the `Return(ByMove(...))` action: ```cpp // When this fires, the unique_ptr<> specified by ByMove(...) will // be returned. EXPECT_CALL(mock_buzzer_, MakeBuzz("world")) .WillOnce(Return(ByMove(MakeUnique(AccessLevel::kInternal)))); EXPECT_NE(nullptr, mock_buzzer_.MakeBuzz("world")); ``` Note that `ByMove()` is essential here - if you drop it, the code won’t compile. Quiz time! What do you think will happen if a `Return(ByMove(...))` action is performed more than once (e.g. you write `.WillRepeatedly(Return(ByMove(...)));`)? Come think of it, after the first time the action runs, the source value will be consumed (since it’s a move-only value), so the next time around, there’s no value to move from -- you’ll get a run-time error that `Return(ByMove(...))` can only be run once. If you need your mock method to do more than just moving a pre-defined value, remember that you can always use a lambda or a callable object, which can do pretty much anything you want: ```cpp EXPECT_CALL(mock_buzzer_, MakeBuzz("x")) .WillRepeatedly([](StringPiece text) { return MakeUnique(AccessLevel::kInternal); }); EXPECT_NE(nullptr, mock_buzzer_.MakeBuzz("x")); EXPECT_NE(nullptr, mock_buzzer_.MakeBuzz("x")); ``` Every time this `EXPECT_CALL` fires, a new `unique_ptr` will be created and returned. You cannot do this with `Return(ByMove(...))`. That covers returning move-only values; but how do we work with methods accepting move-only arguments? The answer is that they work normally, although some actions will not compile when any of method's arguments are move-only. You can always use `Return`, or a [lambda or functor](#using-functionsmethodsfunctors-as-actions): ```cpp using ::testing::Unused; EXPECT_CALL(mock_buzzer_, ShareBuzz(NotNull(), _)) .WillOnce(Return(true)); EXPECT_TRUE(mock_buzzer_.ShareBuzz(MakeUnique(AccessLevel::kInternal)), 0); EXPECT_CALL(mock_buzzer_, ShareBuzz(_, _)) .WillOnce( [](std::unique_ptr buzz, Unused) { return buzz != nullptr; }); EXPECT_FALSE(mock_buzzer_.ShareBuzz(nullptr, 0)); ``` Many built-in actions (`WithArgs`, `WithoutArgs`,`DeleteArg`, `SaveArg`, ...) could in principle support move-only arguments, but the support for this is not implemented yet. If this is blocking you, please file a bug. A few actions (e.g. `DoAll`) copy their arguments internally, so they can never work with non-copyable objects; you'll have to use functors instead. ##### Legacy workarounds for move-only types Support for move-only function arguments was only introduced to gMock in April 2017. In older code, you may encounter the following workaround for the lack of this feature (it is no longer necessary - we're including it just for reference): ```cpp class MockBuzzer : public Buzzer { public: MOCK_METHOD2(DoShareBuzz, bool(Buzz* buzz, Time timestamp)); bool ShareBuzz(std::unique_ptr buzz, Time timestamp) override { return DoShareBuzz(buzz.get(), timestamp); } }; ``` The trick is to delegate the `ShareBuzz()` method to a mock method (let’s call it `DoShareBuzz()`) that does not take move-only parameters. Then, instead of setting expectations on `ShareBuzz()`, you set them on the `DoShareBuzz()` mock method: ```cpp MockBuzzer mock_buzzer_; EXPECT_CALL(mock_buzzer_, DoShareBuzz(NotNull(), _)); // When one calls ShareBuzz() on the MockBuzzer like this, the call is // forwarded to DoShareBuzz(), which is mocked. Therefore this statement // will trigger the above EXPECT_CALL. mock_buzzer_.ShareBuzz(MakeUnique(AccessLevel::kInternal), 0); ``` ## Making the Compilation Faster ## Believe it or not, the _vast majority_ of the time spent on compiling a mock class is in generating its constructor and destructor, as they perform non-trivial tasks (e.g. verification of the expectations). What's more, mock methods with different signatures have different types and thus their constructors/destructors need to be generated by the compiler separately. As a result, if you mock many different types of methods, compiling your mock class can get really slow. If you are experiencing slow compilation, you can move the definition of your mock class' constructor and destructor out of the class body and into a `.cpp` file. This way, even if you `#include` your mock class in N files, the compiler only needs to generate its constructor and destructor once, resulting in a much faster compilation. Let's illustrate the idea using an example. Here's the definition of a mock class before applying this recipe: ```cpp // File mock_foo.h. ... class MockFoo : public Foo { public: // Since we don't declare the constructor or the destructor, // the compiler will generate them in every translation unit // where this mock class is used. MOCK_METHOD0(DoThis, int()); MOCK_METHOD1(DoThat, bool(const char* str)); ... more mock methods ... }; ``` After the change, it would look like: ```cpp // File mock_foo.h. ... class MockFoo : public Foo { public: // The constructor and destructor are declared, but not defined, here. MockFoo(); virtual ~MockFoo(); MOCK_METHOD0(DoThis, int()); MOCK_METHOD1(DoThat, bool(const char* str)); ... more mock methods ... }; ``` and ```cpp // File mock_foo.cpp. #include "path/to/mock_foo.h" // The definitions may appear trivial, but the functions actually do a // lot of things through the constructors/destructors of the member // variables used to implement the mock methods. MockFoo::MockFoo() {} MockFoo::~MockFoo() {} ``` ## Forcing a Verification ## When it's being destroyed, your friendly mock object will automatically verify that all expectations on it have been satisfied, and will generate [Google Test](../../googletest/) failures if not. This is convenient as it leaves you with one less thing to worry about. That is, unless you are not sure if your mock object will be destroyed. How could it be that your mock object won't eventually be destroyed? Well, it might be created on the heap and owned by the code you are testing. Suppose there's a bug in that code and it doesn't delete the mock object properly - you could end up with a passing test when there's actually a bug. Using a heap checker is a good idea and can alleviate the concern, but its implementation may not be 100% reliable. So, sometimes you do want to _force_ Google Mock to verify a mock object before it is (hopefully) destructed. You can do this with `Mock::VerifyAndClearExpectations(&mock_object)`: ```cpp TEST(MyServerTest, ProcessesRequest) { using ::testing::Mock; MockFoo* const foo = new MockFoo; EXPECT_CALL(*foo, ...)...; // ... other expectations ... // server now owns foo. MyServer server(foo); server.ProcessRequest(...); // In case that server's destructor will forget to delete foo, // this will verify the expectations anyway. Mock::VerifyAndClearExpectations(foo); } // server is destroyed when it goes out of scope here. ``` **Tip:** The `Mock::VerifyAndClearExpectations()` function returns a `bool` to indicate whether the verification was successful (`true` for yes), so you can wrap that function call inside a `ASSERT_TRUE()` if there is no point going further when the verification has failed. ## Using Check Points ## Sometimes you may want to "reset" a mock object at various check points in your test: at each check point, you verify that all existing expectations on the mock object have been satisfied, and then you set some new expectations on it as if it's newly created. This allows you to work with a mock object in "phases" whose sizes are each manageable. One such scenario is that in your test's `SetUp()` function, you may want to put the object you are testing into a certain state, with the help from a mock object. Once in the desired state, you want to clear all expectations on the mock, such that in the `TEST_F` body you can set fresh expectations on it. As you may have figured out, the `Mock::VerifyAndClearExpectations()` function we saw in the previous recipe can help you here. Or, if you are using `ON_CALL()` to set default actions on the mock object and want to clear the default actions as well, use `Mock::VerifyAndClear(&mock_object)` instead. This function does what `Mock::VerifyAndClearExpectations(&mock_object)` does and returns the same `bool`, **plus** it clears the `ON_CALL()` statements on `mock_object` too. Another trick you can use to achieve the same effect is to put the expectations in sequences and insert calls to a dummy "check-point" function at specific places. Then you can verify that the mock function calls do happen at the right time. For example, if you are exercising code: ```cpp Foo(1); Foo(2); Foo(3); ``` and want to verify that `Foo(1)` and `Foo(3)` both invoke `mock.Bar("a")`, but `Foo(2)` doesn't invoke anything. You can write: ```cpp using ::testing::MockFunction; TEST(FooTest, InvokesBarCorrectly) { MyMock mock; // Class MockFunction has exactly one mock method. It is named // Call() and has type F. MockFunction check; { InSequence s; EXPECT_CALL(mock, Bar("a")); EXPECT_CALL(check, Call("1")); EXPECT_CALL(check, Call("2")); EXPECT_CALL(mock, Bar("a")); } Foo(1); check.Call("1"); Foo(2); check.Call("2"); Foo(3); } ``` The expectation spec says that the first `Bar("a")` must happen before check point "1", the second `Bar("a")` must happen after check point "2", and nothing should happen between the two check points. The explicit check points make it easy to tell which `Bar("a")` is called by which call to `Foo()`. ## Mocking Destructors ## Sometimes you want to make sure a mock object is destructed at the right time, e.g. after `bar->A()` is called but before `bar->B()` is called. We already know that you can specify constraints on the order of mock function calls, so all we need to do is to mock the destructor of the mock function. This sounds simple, except for one problem: a destructor is a special function with special syntax and special semantics, and the `MOCK_METHOD0` macro doesn't work for it: ```cpp MOCK_METHOD0(~MockFoo, void()); // Won't compile! ``` The good news is that you can use a simple pattern to achieve the same effect. First, add a mock function `Die()` to your mock class and call it in the destructor, like this: ```cpp class MockFoo : public Foo { ... // Add the following two lines to the mock class. MOCK_METHOD0(Die, void()); virtual ~MockFoo() { Die(); } }; ``` (If the name `Die()` clashes with an existing symbol, choose another name.) Now, we have translated the problem of testing when a `MockFoo` object dies to testing when its `Die()` method is called: ```cpp MockFoo* foo = new MockFoo; MockBar* bar = new MockBar; ... { InSequence s; // Expects *foo to die after bar->A() and before bar->B(). EXPECT_CALL(*bar, A()); EXPECT_CALL(*foo, Die()); EXPECT_CALL(*bar, B()); } ``` And that's that. ## Using Google Mock and Threads ## **IMPORTANT NOTE:** What we describe in this recipe is **ONLY** true on platforms where Google Mock is thread-safe. Currently these are only platforms that support the pthreads library (this includes Linux and Mac). To make it thread-safe on other platforms we only need to implement some synchronization operations in `"gtest/internal/gtest-port.h"`. In a **unit** test, it's best if you could isolate and test a piece of code in a single-threaded context. That avoids race conditions and dead locks, and makes debugging your test much easier. Yet many programs are multi-threaded, and sometimes to test something we need to pound on it from more than one thread. Google Mock works for this purpose too. Remember the steps for using a mock: 1. Create a mock object `foo`. 1. Set its default actions and expectations using `ON_CALL()` and `EXPECT_CALL()`. 1. The code under test calls methods of `foo`. 1. Optionally, verify and reset the mock. 1. Destroy the mock yourself, or let the code under test destroy it. The destructor will automatically verify it. If you follow the following simple rules, your mocks and threads can live happily together: * Execute your _test code_ (as opposed to the code being tested) in _one_ thread. This makes your test easy to follow. * Obviously, you can do step #1 without locking. * When doing step #2 and #5, make sure no other thread is accessing `foo`. Obvious too, huh? * #3 and #4 can be done either in one thread or in multiple threads - anyway you want. Google Mock takes care of the locking, so you don't have to do any - unless required by your test logic. If you violate the rules (for example, if you set expectations on a mock while another thread is calling its methods), you get undefined behavior. That's not fun, so don't do it. Google Mock guarantees that the action for a mock function is done in the same thread that called the mock function. For example, in ```cpp EXPECT_CALL(mock, Foo(1)) .WillOnce(action1); EXPECT_CALL(mock, Foo(2)) .WillOnce(action2); ``` if `Foo(1)` is called in thread 1 and `Foo(2)` is called in thread 2, Google Mock will execute `action1` in thread 1 and `action2` in thread 2. Google Mock does _not_ impose a sequence on actions performed in different threads (doing so may create deadlocks as the actions may need to cooperate). This means that the execution of `action1` and `action2` in the above example _may_ interleave. If this is a problem, you should add proper synchronization logic to `action1` and `action2` to make the test thread-safe. Also, remember that `DefaultValue` is a global resource that potentially affects _all_ living mock objects in your program. Naturally, you won't want to mess with it from multiple threads or when there still are mocks in action. ## Controlling How Much Information Google Mock Prints ## When Google Mock sees something that has the potential of being an error (e.g. a mock function with no expectation is called, a.k.a. an uninteresting call, which is allowed but perhaps you forgot to explicitly ban the call), it prints some warning messages, including the arguments of the function and the return value. Hopefully this will remind you to take a look and see if there is indeed a problem. Sometimes you are confident that your tests are correct and may not appreciate such friendly messages. Some other times, you are debugging your tests or learning about the behavior of the code you are testing, and wish you could observe every mock call that happens (including argument values and the return value). Clearly, one size doesn't fit all. You can control how much Google Mock tells you using the `--gmock_verbose=LEVEL` command-line flag, where `LEVEL` is a string with three possible values: * `info`: Google Mock will print all informational messages, warnings, and errors (most verbose). At this setting, Google Mock will also log any calls to the `ON_CALL/EXPECT_CALL` macros. * `warning`: Google Mock will print both warnings and errors (less verbose). This is the default. * `error`: Google Mock will print errors only (least verbose). Alternatively, you can adjust the value of that flag from within your tests like so: ```cpp ::testing::FLAGS_gmock_verbose = "error"; ``` Now, judiciously use the right flag to enable Google Mock serve you better! ## Gaining Super Vision into Mock Calls ## You have a test using Google Mock. It fails: Google Mock tells you that some expectations aren't satisfied. However, you aren't sure why: Is there a typo somewhere in the matchers? Did you mess up the order of the `EXPECT_CALL`s? Or is the code under test doing something wrong? How can you find out the cause? Won't it be nice if you have X-ray vision and can actually see the trace of all `EXPECT_CALL`s and mock method calls as they are made? For each call, would you like to see its actual argument values and which `EXPECT_CALL` Google Mock thinks it matches? You can unlock this power by running your test with the `--gmock_verbose=info` flag. For example, given the test program: ```cpp using testing::_; using testing::HasSubstr; using testing::Return; class MockFoo { public: MOCK_METHOD2(F, void(const string& x, const string& y)); }; TEST(Foo, Bar) { MockFoo mock; EXPECT_CALL(mock, F(_, _)).WillRepeatedly(Return()); EXPECT_CALL(mock, F("a", "b")); EXPECT_CALL(mock, F("c", HasSubstr("d"))); mock.F("a", "good"); mock.F("a", "b"); } ``` if you run it with `--gmock_verbose=info`, you will see this output: ``` [ RUN ] Foo.Bar foo_test.cc:14: EXPECT_CALL(mock, F(_, _)) invoked foo_test.cc:15: EXPECT_CALL(mock, F("a", "b")) invoked foo_test.cc:16: EXPECT_CALL(mock, F("c", HasSubstr("d"))) invoked foo_test.cc:14: Mock function call matches EXPECT_CALL(mock, F(_, _))... Function call: F(@0x7fff7c8dad40"a", @0x7fff7c8dad10"good") foo_test.cc:15: Mock function call matches EXPECT_CALL(mock, F("a", "b"))... Function call: F(@0x7fff7c8dada0"a", @0x7fff7c8dad70"b") foo_test.cc:16: Failure Actual function call count doesn't match EXPECT_CALL(mock, F("c", HasSubstr("d")))... Expected: to be called once Actual: never called - unsatisfied and active [ FAILED ] Foo.Bar ``` Suppose the bug is that the `"c"` in the third `EXPECT_CALL` is a typo and should actually be `"a"`. With the above message, you should see that the actual `F("a", "good")` call is matched by the first `EXPECT_CALL`, not the third as you thought. From that it should be obvious that the third `EXPECT_CALL` is written wrong. Case solved. ## Running Tests in Emacs ## If you build and run your tests in Emacs, the source file locations of Google Mock and [Google Test](../../googletest/) errors will be highlighted. Just press `` on one of them and you'll be taken to the offending line. Or, you can just type `C-x `` to jump to the next error. To make it even easier, you can add the following lines to your `~/.emacs` file: ``` (global-set-key "\M-m" 'compile) ; m is for make (global-set-key [M-down] 'next-error) (global-set-key [M-up] '(lambda () (interactive) (next-error -1))) ``` Then you can type `M-m` to start a build, or `M-up`/`M-down` to move back and forth between errors. ## Fusing Google Mock Source Files ## Google Mock's implementation consists of dozens of files (excluding its own tests). Sometimes you may want them to be packaged up in fewer files instead, such that you can easily copy them to a new machine and start hacking there. For this we provide an experimental Python script `fuse_gmock_files.py` in the `scripts/` directory (starting with release 1.2.0). Assuming you have Python 2.4 or above installed on your machine, just go to that directory and run ``` python fuse_gmock_files.py OUTPUT_DIR ``` and you should see an `OUTPUT_DIR` directory being created with files `gtest/gtest.h`, `gmock/gmock.h`, and `gmock-gtest-all.cc` in it. These three files contain everything you need to use Google Mock (and Google Test). Just copy them to anywhere you want and you are ready to write tests and use mocks. # Extending Google Mock # ## Writing New Matchers Quickly ## The `MATCHER*` family of macros can be used to define custom matchers easily. The syntax: ```cpp MATCHER(name, description_string_expression) { statements; } ``` will define a matcher with the given name that executes the statements, which must return a `bool` to indicate if the match succeeds. Inside the statements, you can refer to the value being matched by `arg`, and refer to its type by `arg_type`. The description string is a `string`-typed expression that documents what the matcher does, and is used to generate the failure message when the match fails. It can (and should) reference the special `bool` variable `negation`, and should evaluate to the description of the matcher when `negation` is `false`, or that of the matcher's negation when `negation` is `true`. For convenience, we allow the description string to be empty (`""`), in which case Google Mock will use the sequence of words in the matcher name as the description. For example: ```cpp MATCHER(IsDivisibleBy7, "") { return (arg % 7) == 0; } ``` allows you to write ```cpp // Expects mock_foo.Bar(n) to be called where n is divisible by 7. EXPECT_CALL(mock_foo, Bar(IsDivisibleBy7())); ``` or, ```cpp using ::testing::Not; ... EXPECT_THAT(some_expression, IsDivisibleBy7()); EXPECT_THAT(some_other_expression, Not(IsDivisibleBy7())); ``` If the above assertions fail, they will print something like: ``` Value of: some_expression Expected: is divisible by 7 Actual: 27 ... Value of: some_other_expression Expected: not (is divisible by 7) Actual: 21 ``` where the descriptions `"is divisible by 7"` and `"not (is divisible by 7)"` are automatically calculated from the matcher name `IsDivisibleBy7`. As you may have noticed, the auto-generated descriptions (especially those for the negation) may not be so great. You can always override them with a string expression of your own: ```cpp MATCHER(IsDivisibleBy7, std::string(negation ? "isn't" : "is") + " divisible by 7") { return (arg % 7) == 0; } ``` Optionally, you can stream additional information to a hidden argument named `result_listener` to explain the match result. For example, a better definition of `IsDivisibleBy7` is: ```cpp MATCHER(IsDivisibleBy7, "") { if ((arg % 7) == 0) return true; *result_listener << "the remainder is " << (arg % 7); return false; } ``` With this definition, the above assertion will give a better message: ``` Value of: some_expression Expected: is divisible by 7 Actual: 27 (the remainder is 6) ``` You should let `MatchAndExplain()` print _any additional information_ that can help a user understand the match result. Note that it should explain why the match succeeds in case of a success (unless it's obvious) - this is useful when the matcher is used inside `Not()`. There is no need to print the argument value itself, as Google Mock already prints it for you. **Notes:** 1. The type of the value being matched (`arg_type`) is determined by the context in which you use the matcher and is supplied to you by the compiler, so you don't need to worry about declaring it (nor can you). This allows the matcher to be polymorphic. For example, `IsDivisibleBy7()` can be used to match any type where the value of `(arg % 7) == 0` can be implicitly converted to a `bool`. In the `Bar(IsDivisibleBy7())` example above, if method `Bar()` takes an `int`, `arg_type` will be `int`; if it takes an `unsigned long`, `arg_type` will be `unsigned long`; and so on. 1. Google Mock doesn't guarantee when or how many times a matcher will be invoked. Therefore the matcher logic must be _purely functional_ (i.e. it cannot have any side effect, and the result must not depend on anything other than the value being matched and the matcher parameters). This requirement must be satisfied no matter how you define the matcher (e.g. using one of the methods described in the following recipes). In particular, a matcher can never call a mock function, as that will affect the state of the mock object and Google Mock. ## Writing New Parameterized Matchers Quickly ## Sometimes you'll want to define a matcher that has parameters. For that you can use the macro: ```cpp MATCHER_P(name, param_name, description_string) { statements; } ``` where the description string can be either `""` or a string expression that references `negation` and `param_name`. For example: ```cpp MATCHER_P(HasAbsoluteValue, value, "") { return abs(arg) == value; } ``` will allow you to write: ```cpp EXPECT_THAT(Blah("a"), HasAbsoluteValue(n)); ``` which may lead to this message (assuming `n` is 10): ``` Value of: Blah("a") Expected: has absolute value 10 Actual: -9 ``` Note that both the matcher description and its parameter are printed, making the message human-friendly. In the matcher definition body, you can write `foo_type` to reference the type of a parameter named `foo`. For example, in the body of `MATCHER_P(HasAbsoluteValue, value)` above, you can write `value_type` to refer to the type of `value`. Google Mock also provides `MATCHER_P2`, `MATCHER_P3`, ..., up to `MATCHER_P10` to support multi-parameter matchers: ```cpp MATCHER_Pk(name, param_1, ..., param_k, description_string) { statements; } ``` Please note that the custom description string is for a particular **instance** of the matcher, where the parameters have been bound to actual values. Therefore usually you'll want the parameter values to be part of the description. Google Mock lets you do that by referencing the matcher parameters in the description string expression. For example, ```cpp using ::testing::PrintToString; MATCHER_P2(InClosedRange, low, hi, std::string(negation ? "isn't" : "is") + " in range [" + PrintToString(low) + ", " + PrintToString(hi) + "]") { return low <= arg && arg <= hi; } ... EXPECT_THAT(3, InClosedRange(4, 6)); ``` would generate a failure that contains the message: ``` Expected: is in range [4, 6] ``` If you specify `""` as the description, the failure message will contain the sequence of words in the matcher name followed by the parameter values printed as a tuple. For example, ```cpp MATCHER_P2(InClosedRange, low, hi, "") { ... } ... EXPECT_THAT(3, InClosedRange(4, 6)); ``` would generate a failure that contains the text: ``` Expected: in closed range (4, 6) ``` For the purpose of typing, you can view ```cpp MATCHER_Pk(Foo, p1, ..., pk, description_string) { ... } ``` as shorthand for ```cpp template FooMatcherPk Foo(p1_type p1, ..., pk_type pk) { ... } ``` When you write `Foo(v1, ..., vk)`, the compiler infers the types of the parameters `v1`, ..., and `vk` for you. If you are not happy with the result of the type inference, you can specify the types by explicitly instantiating the template, as in `Foo(5, false)`. As said earlier, you don't get to (or need to) specify `arg_type` as that's determined by the context in which the matcher is used. You can assign the result of expression `Foo(p1, ..., pk)` to a variable of type `FooMatcherPk`. This can be useful when composing matchers. Matchers that don't have a parameter or have only one parameter have special types: you can assign `Foo()` to a `FooMatcher`-typed variable, and assign `Foo(p)` to a `FooMatcherP`-typed variable. While you can instantiate a matcher template with reference types, passing the parameters by pointer usually makes your code more readable. If, however, you still want to pass a parameter by reference, be aware that in the failure message generated by the matcher you will see the value of the referenced object but not its address. You can overload matchers with different numbers of parameters: ```cpp MATCHER_P(Blah, a, description_string_1) { ... } MATCHER_P2(Blah, a, b, description_string_2) { ... } ``` While it's tempting to always use the `MATCHER*` macros when defining a new matcher, you should also consider implementing `MatcherInterface` or using `MakePolymorphicMatcher()` instead (see the recipes that follow), especially if you need to use the matcher a lot. While these approaches require more work, they give you more control on the types of the value being matched and the matcher parameters, which in general leads to better compiler error messages that pay off in the long run. They also allow overloading matchers based on parameter types (as opposed to just based on the number of parameters). ## Writing New Monomorphic Matchers ## A matcher of argument type `T` implements `::testing::MatcherInterface` and does two things: it tests whether a value of type `T` matches the matcher, and can describe what kind of values it matches. The latter ability is used for generating readable error messages when expectations are violated. The interface looks like this: ```cpp class MatchResultListener { public: ... // Streams x to the underlying ostream; does nothing if the ostream // is NULL. template MatchResultListener& operator<<(const T& x); // Returns the underlying ostream. ::std::ostream* stream(); }; template class MatcherInterface { public: virtual ~MatcherInterface(); // Returns true iff the matcher matches x; also explains the match // result to 'listener'. virtual bool MatchAndExplain(T x, MatchResultListener* listener) const = 0; // Describes this matcher to an ostream. virtual void DescribeTo(::std::ostream* os) const = 0; // Describes the negation of this matcher to an ostream. virtual void DescribeNegationTo(::std::ostream* os) const; }; ``` If you need a custom matcher but `Truly()` is not a good option (for example, you may not be happy with the way `Truly(predicate)` describes itself, or you may want your matcher to be polymorphic as `Eq(value)` is), you can define a matcher to do whatever you want in two steps: first implement the matcher interface, and then define a factory function to create a matcher instance. The second step is not strictly needed but it makes the syntax of using the matcher nicer. For example, you can define a matcher to test whether an `int` is divisible by 7 and then use it like this: ```cpp using ::testing::MakeMatcher; using ::testing::Matcher; using ::testing::MatcherInterface; using ::testing::MatchResultListener; class DivisibleBy7Matcher : public MatcherInterface { public: virtual bool MatchAndExplain(int n, MatchResultListener* listener) const { return (n % 7) == 0; } virtual void DescribeTo(::std::ostream* os) const { *os << "is divisible by 7"; } virtual void DescribeNegationTo(::std::ostream* os) const { *os << "is not divisible by 7"; } }; inline Matcher DivisibleBy7() { return MakeMatcher(new DivisibleBy7Matcher); } ... EXPECT_CALL(foo, Bar(DivisibleBy7())); ``` You may improve the matcher message by streaming additional information to the `listener` argument in `MatchAndExplain()`: ```cpp class DivisibleBy7Matcher : public MatcherInterface { public: virtual bool MatchAndExplain(int n, MatchResultListener* listener) const { const int remainder = n % 7; if (remainder != 0) { *listener << "the remainder is " << remainder; } return remainder == 0; } ... }; ``` Then, `EXPECT_THAT(x, DivisibleBy7());` may general a message like this: ``` Value of: x Expected: is divisible by 7 Actual: 23 (the remainder is 2) ``` ## Writing New Polymorphic Matchers ## You've learned how to write your own matchers in the previous recipe. Just one problem: a matcher created using `MakeMatcher()` only works for one particular type of arguments. If you want a _polymorphic_ matcher that works with arguments of several types (for instance, `Eq(x)` can be used to match a `value` as long as `value` == `x` compiles -- `value` and `x` don't have to share the same type), you can learn the trick from `"gmock/gmock-matchers.h"` but it's a bit involved. Fortunately, most of the time you can define a polymorphic matcher easily with the help of `MakePolymorphicMatcher()`. Here's how you can define `NotNull()` as an example: ```cpp using ::testing::MakePolymorphicMatcher; using ::testing::MatchResultListener; using ::testing::NotNull; using ::testing::PolymorphicMatcher; class NotNullMatcher { public: // To implement a polymorphic matcher, first define a COPYABLE class // that has three members MatchAndExplain(), DescribeTo(), and // DescribeNegationTo(), like the following. // In this example, we want to use NotNull() with any pointer, so // MatchAndExplain() accepts a pointer of any type as its first argument. // In general, you can define MatchAndExplain() as an ordinary method or // a method template, or even overload it. template bool MatchAndExplain(T* p, MatchResultListener* /* listener */) const { return p != NULL; } // Describes the property of a value matching this matcher. void DescribeTo(::std::ostream* os) const { *os << "is not NULL"; } // Describes the property of a value NOT matching this matcher. void DescribeNegationTo(::std::ostream* os) const { *os << "is NULL"; } }; // To construct a polymorphic matcher, pass an instance of the class // to MakePolymorphicMatcher(). Note the return type. inline PolymorphicMatcher NotNull() { return MakePolymorphicMatcher(NotNullMatcher()); } ... EXPECT_CALL(foo, Bar(NotNull())); // The argument must be a non-NULL pointer. ``` **Note:** Your polymorphic matcher class does **not** need to inherit from `MatcherInterface` or any other class, and its methods do **not** need to be virtual. Like in a monomorphic matcher, you may explain the match result by streaming additional information to the `listener` argument in `MatchAndExplain()`. ## Writing New Cardinalities ## A cardinality is used in `Times()` to tell Google Mock how many times you expect a call to occur. It doesn't have to be exact. For example, you can say `AtLeast(5)` or `Between(2, 4)`. If the built-in set of cardinalities doesn't suit you, you are free to define your own by implementing the following interface (in namespace `testing`): ```cpp class CardinalityInterface { public: virtual ~CardinalityInterface(); // Returns true iff call_count calls will satisfy this cardinality. virtual bool IsSatisfiedByCallCount(int call_count) const = 0; // Returns true iff call_count calls will saturate this cardinality. virtual bool IsSaturatedByCallCount(int call_count) const = 0; // Describes self to an ostream. virtual void DescribeTo(::std::ostream* os) const = 0; }; ``` For example, to specify that a call must occur even number of times, you can write ```cpp using ::testing::Cardinality; using ::testing::CardinalityInterface; using ::testing::MakeCardinality; class EvenNumberCardinality : public CardinalityInterface { public: virtual bool IsSatisfiedByCallCount(int call_count) const { return (call_count % 2) == 0; } virtual bool IsSaturatedByCallCount(int call_count) const { return false; } virtual void DescribeTo(::std::ostream* os) const { *os << "called even number of times"; } }; Cardinality EvenNumber() { return MakeCardinality(new EvenNumberCardinality); } ... EXPECT_CALL(foo, Bar(3)) .Times(EvenNumber()); ``` ## Writing New Actions Quickly ## If the built-in actions don't work for you, and you find it inconvenient to use `Invoke()`, you can use a macro from the `ACTION*` family to quickly define a new action that can be used in your code as if it's a built-in action. By writing ```cpp ACTION(name) { statements; } ``` in a namespace scope (i.e. not inside a class or function), you will define an action with the given name that executes the statements. The value returned by `statements` will be used as the return value of the action. Inside the statements, you can refer to the K-th (0-based) argument of the mock function as `argK`. For example: ```cpp ACTION(IncrementArg1) { return ++(*arg1); } ``` allows you to write ```cpp ... WillOnce(IncrementArg1()); ``` Note that you don't need to specify the types of the mock function arguments. Rest assured that your code is type-safe though: you'll get a compiler error if `*arg1` doesn't support the `++` operator, or if the type of `++(*arg1)` isn't compatible with the mock function's return type. Another example: ```cpp ACTION(Foo) { (*arg2)(5); Blah(); *arg1 = 0; return arg0; } ``` defines an action `Foo()` that invokes argument #2 (a function pointer) with 5, calls function `Blah()`, sets the value pointed to by argument #1 to 0, and returns argument #0. For more convenience and flexibility, you can also use the following pre-defined symbols in the body of `ACTION`: | `argK_type` | The type of the K-th (0-based) argument of the mock function | |:----------------|:-------------------------------------------------------------| | `args` | All arguments of the mock function as a tuple | | `args_type` | The type of all arguments of the mock function as a tuple | | `return_type` | The return type of the mock function | | `function_type` | The type of the mock function | For example, when using an `ACTION` as a stub action for mock function: ```cpp int DoSomething(bool flag, int* ptr); ``` we have: | **Pre-defined Symbol** | **Is Bound To** | |:-----------------------|:----------------| | `arg0` | the value of `flag` | | `arg0_type` | the type `bool` | | `arg1` | the value of `ptr` | | `arg1_type` | the type `int*` | | `args` | the tuple `(flag, ptr)` | | `args_type` | the type `::testing::tuple` | | `return_type` | the type `int` | | `function_type` | the type `int(bool, int*)` | ## Writing New Parameterized Actions Quickly ## Sometimes you'll want to parameterize an action you define. For that we have another macro ```cpp ACTION_P(name, param) { statements; } ``` For example, ```cpp ACTION_P(Add, n) { return arg0 + n; } ``` will allow you to write ```cpp // Returns argument #0 + 5. ... WillOnce(Add(5)); ``` For convenience, we use the term _arguments_ for the values used to invoke the mock function, and the term _parameters_ for the values used to instantiate an action. Note that you don't need to provide the type of the parameter either. Suppose the parameter is named `param`, you can also use the Google-Mock-defined symbol `param_type` to refer to the type of the parameter as inferred by the compiler. For example, in the body of `ACTION_P(Add, n)` above, you can write `n_type` for the type of `n`. Google Mock also provides `ACTION_P2`, `ACTION_P3`, and etc to support multi-parameter actions. For example, ```cpp ACTION_P2(ReturnDistanceTo, x, y) { double dx = arg0 - x; double dy = arg1 - y; return sqrt(dx*dx + dy*dy); } ``` lets you write ```cpp ... WillOnce(ReturnDistanceTo(5.0, 26.5)); ``` You can view `ACTION` as a degenerated parameterized action where the number of parameters is 0. You can also easily define actions overloaded on the number of parameters: ```cpp ACTION_P(Plus, a) { ... } ACTION_P2(Plus, a, b) { ... } ``` ## Restricting the Type of an Argument or Parameter in an ACTION ## For maximum brevity and reusability, the `ACTION*` macros don't ask you to provide the types of the mock function arguments and the action parameters. Instead, we let the compiler infer the types for us. Sometimes, however, we may want to be more explicit about the types. There are several tricks to do that. For example: ```cpp ACTION(Foo) { // Makes sure arg0 can be converted to int. int n = arg0; ... use n instead of arg0 here ... } ACTION_P(Bar, param) { // Makes sure the type of arg1 is const char*. ::testing::StaticAssertTypeEq(); // Makes sure param can be converted to bool. bool flag = param; } ``` where `StaticAssertTypeEq` is a compile-time assertion in Google Test that verifies two types are the same. ## Writing New Action Templates Quickly ## Sometimes you want to give an action explicit template parameters that cannot be inferred from its value parameters. `ACTION_TEMPLATE()` supports that and can be viewed as an extension to `ACTION()` and `ACTION_P*()`. The syntax: ```cpp ACTION_TEMPLATE(ActionName, HAS_m_TEMPLATE_PARAMS(kind1, name1, ..., kind_m, name_m), AND_n_VALUE_PARAMS(p1, ..., p_n)) { statements; } ``` defines an action template that takes _m_ explicit template parameters and _n_ value parameters, where _m_ is between 1 and 10, and _n_ is between 0 and 10. `name_i` is the name of the i-th template parameter, and `kind_i` specifies whether it's a `typename`, an integral constant, or a template. `p_i` is the name of the i-th value parameter. Example: ```cpp // DuplicateArg(output) converts the k-th argument of the mock // function to type T and copies it to *output. ACTION_TEMPLATE(DuplicateArg, // Note the comma between int and k: HAS_2_TEMPLATE_PARAMS(int, k, typename, T), AND_1_VALUE_PARAMS(output)) { *output = T(::testing::get(args)); } ``` To create an instance of an action template, write: ```cpp ActionName(v1, ..., v_n) ``` where the `t`s are the template arguments and the `v`s are the value arguments. The value argument types are inferred by the compiler. For example: ```cpp using ::testing::_; ... int n; EXPECT_CALL(mock, Foo(_, _)) .WillOnce(DuplicateArg<1, unsigned char>(&n)); ``` If you want to explicitly specify the value argument types, you can provide additional template arguments: ```cpp ActionName(v1, ..., v_n) ``` where `u_i` is the desired type of `v_i`. `ACTION_TEMPLATE` and `ACTION`/`ACTION_P*` can be overloaded on the number of value parameters, but not on the number of template parameters. Without the restriction, the meaning of the following is unclear: ```cpp OverloadedAction(x); ``` Are we using a single-template-parameter action where `bool` refers to the type of `x`, or a two-template-parameter action where the compiler is asked to infer the type of `x`? ## Using the ACTION Object's Type ## If you are writing a function that returns an `ACTION` object, you'll need to know its type. The type depends on the macro used to define the action and the parameter types. The rule is relatively simple: | **Given Definition** | **Expression** | **Has Type** | |:---------------------|:---------------|:-------------| | `ACTION(Foo)` | `Foo()` | `FooAction` | | `ACTION_TEMPLATE(Foo, HAS_m_TEMPLATE_PARAMS(...), AND_0_VALUE_PARAMS())` | `Foo()` | `FooAction` | | `ACTION_P(Bar, param)` | `Bar(int_value)` | `BarActionP` | | `ACTION_TEMPLATE(Bar, HAS_m_TEMPLATE_PARAMS(...), AND_1_VALUE_PARAMS(p1))` | `Bar(int_value)` | `FooActionP` | | `ACTION_P2(Baz, p1, p2)` | `Baz(bool_value, int_value)` | `BazActionP2` | | `ACTION_TEMPLATE(Baz, HAS_m_TEMPLATE_PARAMS(...), AND_2_VALUE_PARAMS(p1, p2))`| `Baz(bool_value, int_value)` | `FooActionP2` | | ... | ... | ... | Note that we have to pick different suffixes (`Action`, `ActionP`, `ActionP2`, and etc) for actions with different numbers of value parameters, or the action definitions cannot be overloaded on the number of them. ## Writing New Monomorphic Actions ## While the `ACTION*` macros are very convenient, sometimes they are inappropriate. For example, despite the tricks shown in the previous recipes, they don't let you directly specify the types of the mock function arguments and the action parameters, which in general leads to unoptimized compiler error messages that can baffle unfamiliar users. They also don't allow overloading actions based on parameter types without jumping through some hoops. An alternative to the `ACTION*` macros is to implement `::testing::ActionInterface`, where `F` is the type of the mock function in which the action will be used. For example: ```cpp template class ActionInterface { public: virtual ~ActionInterface(); // Performs the action. Result is the return type of function type // F, and ArgumentTuple is the tuple of arguments of F. // // For example, if F is int(bool, const string&), then Result would // be int, and ArgumentTuple would be ::testing::tuple. virtual Result Perform(const ArgumentTuple& args) = 0; }; using ::testing::_; using ::testing::Action; using ::testing::ActionInterface; using ::testing::MakeAction; typedef int IncrementMethod(int*); class IncrementArgumentAction : public ActionInterface { public: virtual int Perform(const ::testing::tuple& args) { int* p = ::testing::get<0>(args); // Grabs the first argument. return *p++; } }; Action IncrementArgument() { return MakeAction(new IncrementArgumentAction); } ... EXPECT_CALL(foo, Baz(_)) .WillOnce(IncrementArgument()); int n = 5; foo.Baz(&n); // Should return 5 and change n to 6. ``` ## Writing New Polymorphic Actions ## The previous recipe showed you how to define your own action. This is all good, except that you need to know the type of the function in which the action will be used. Sometimes that can be a problem. For example, if you want to use the action in functions with _different_ types (e.g. like `Return()` and `SetArgPointee()`). If an action can be used in several types of mock functions, we say it's _polymorphic_. The `MakePolymorphicAction()` function template makes it easy to define such an action: ```cpp namespace testing { template PolymorphicAction MakePolymorphicAction(const Impl& impl); } // namespace testing ``` As an example, let's define an action that returns the second argument in the mock function's argument list. The first step is to define an implementation class: ```cpp class ReturnSecondArgumentAction { public: template Result Perform(const ArgumentTuple& args) const { // To get the i-th (0-based) argument, use ::testing::get(args). return ::testing::get<1>(args); } }; ``` This implementation class does _not_ need to inherit from any particular class. What matters is that it must have a `Perform()` method template. This method template takes the mock function's arguments as a tuple in a **single** argument, and returns the result of the action. It can be either `const` or not, but must be invokable with exactly one template argument, which is the result type. In other words, you must be able to call `Perform(args)` where `R` is the mock function's return type and `args` is its arguments in a tuple. Next, we use `MakePolymorphicAction()` to turn an instance of the implementation class into the polymorphic action we need. It will be convenient to have a wrapper for this: ```cpp using ::testing::MakePolymorphicAction; using ::testing::PolymorphicAction; PolymorphicAction ReturnSecondArgument() { return MakePolymorphicAction(ReturnSecondArgumentAction()); } ``` Now, you can use this polymorphic action the same way you use the built-in ones: ```cpp using ::testing::_; class MockFoo : public Foo { public: MOCK_METHOD2(DoThis, int(bool flag, int n)); MOCK_METHOD3(DoThat, string(int x, const char* str1, const char* str2)); }; ... MockFoo foo; EXPECT_CALL(foo, DoThis(_, _)) .WillOnce(ReturnSecondArgument()); EXPECT_CALL(foo, DoThat(_, _, _)) .WillOnce(ReturnSecondArgument()); ... foo.DoThis(true, 5); // Will return 5. foo.DoThat(1, "Hi", "Bye"); // Will return "Hi". ``` ## Teaching Google Mock How to Print Your Values ## When an uninteresting or unexpected call occurs, Google Mock prints the argument values and the stack trace to help you debug. Assertion macros like `EXPECT_THAT` and `EXPECT_EQ` also print the values in question when the assertion fails. Google Mock and Google Test do this using Google Test's user-extensible value printer. This printer knows how to print built-in C++ types, native arrays, STL containers, and any type that supports the `<<` operator. For other types, it prints the raw bytes in the value and hopes that you the user can figure it out. [Google Test's advanced guide](../../googletest/docs/advanced.md#teaching-googletest-how-to-print-your-values) explains how to extend the printer to do a better job at printing your particular type than to dump the bytes. diff --git a/googlemock/docs/DesignDoc.md b/googlemock/docs/design_doc.md similarity index 100% rename from googlemock/docs/DesignDoc.md rename to googlemock/docs/design_doc.md diff --git a/googlemock/docs/Documentation.md b/googlemock/docs/documentation.md similarity index 60% rename from googlemock/docs/Documentation.md rename to googlemock/docs/documentation.md index af8a3b90..831598cc 100644 --- a/googlemock/docs/Documentation.md +++ b/googlemock/docs/documentation.md @@ -1,15 +1,16 @@ This page lists all documentation markdown files for Google Mock **(the current git version)** -- **if you use a former version of Google Mock, please read the documentation for that specific version instead (e.g. by checking out the respective git branch/tag).** - * [ForDummies](ForDummies.md) -- start here if you are new to Google Mock. - * [CheatSheet](CheatSheet.md) -- a quick reference. + * [ForDummies](for_dummies.md) -- start here if you are new to Google Mock. + * [CheatSheet](cheat_sheet.md) -- a quick reference. * [CookBook](cook_book.md) -- recipes for doing various tasks using Google Mock. - * [FrequentlyAskedQuestions](FrequentlyAskedQuestions.md) -- check here before asking a question on the mailing list. + * [DesignDoc](design_doc.md) -- design of and rationale behind some Google Mock features. + * [FrequentlyAskedQuestions](frequently_asked_questions.md) and [KnownIssues](known_issues.md) -- check here before asking a question on the mailing list. To contribute code to Google Mock, read: * [CONTRIBUTING](../../CONTRIBUTING.md) -- read this _before_ writing your first patch. * [Pump Manual](../../googletest/docs/pump_manual.md) -- how we generate some of the source files. diff --git a/googlemock/docs/ForDummies.md b/googlemock/docs/for_dummies.md similarity index 98% rename from googlemock/docs/ForDummies.md rename to googlemock/docs/for_dummies.md index c8a83cba..21105312 100644 --- a/googlemock/docs/ForDummies.md +++ b/googlemock/docs/for_dummies.md @@ -1,447 +1,447 @@ -(**Note:** If you get compiler errors that you don't understand, be sure to consult [Google Mock Doctor](FrequentlyAskedQuestions.md#how-am-i-supposed-to-make-sense-of-these-horrible-template-errors).) +(**Note:** If you get compiler errors that you don't understand, be sure to consult [Google Mock Doctor](frequently_asked_questions.md#how-am-i-supposed-to-make-sense-of-these-horrible-template-errors).) # What Is Google C++ Mocking Framework? # When you write a prototype or test, often it's not feasible or wise to rely on real objects entirely. A **mock object** implements the same interface as a real object (so it can be used as one), but lets you specify at run time how it will be used and what it should do (which methods will be called? in which order? how many times? with what arguments? what will they return? etc). **Note:** It is easy to confuse the term _fake objects_ with mock objects. Fakes and mocks actually mean very different things in the Test-Driven Development (TDD) community: * **Fake** objects have working implementations, but usually take some shortcut (perhaps to make the operations less expensive), which makes them not suitable for production. An in-memory file system would be an example of a fake. * **Mocks** are objects pre-programmed with _expectations_, which form a specification of the calls they are expected to receive. If all this seems too abstract for you, don't worry - the most important thing to remember is that a mock allows you to check the _interaction_ between itself and code that uses it. The difference between fakes and mocks will become much clearer once you start to use mocks. **Google C++ Mocking Framework** (or **Google Mock** for short) is a library (sometimes we also call it a "framework" to make it sound cool) for creating mock classes and using them. It does to C++ what [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/) do to Java. Using Google Mock involves three basic steps: 1. Use some simple macros to describe the interface you want to mock, and they will expand to the implementation of your mock class; 1. Create some mock objects and specify its expectations and behavior using an intuitive syntax; 1. Exercise code that uses the mock objects. Google Mock will catch any violation of the expectations as soon as it arises. # Why Google Mock? # While mock objects help you remove unnecessary dependencies in tests and make them fast and reliable, using mocks manually in C++ is _hard_: * Someone has to implement the mocks. The job is usually tedious and error-prone. No wonder people go great distances to avoid it. * The quality of those manually written mocks is a bit, uh, unpredictable. You may see some really polished ones, but you may also see some that were hacked up in a hurry and have all sorts of ad-hoc restrictions. * The knowledge you gained from using one mock doesn't transfer to the next. In contrast, Java and Python programmers have some fine mock frameworks, which automate the creation of mocks. As a result, mocking is a proven effective technique and widely adopted practice in those communities. Having the right tool absolutely makes the difference. Google Mock was built to help C++ programmers. It was inspired by [jMock](http://www.jmock.org/) and [EasyMock](http://www.easymock.org/), but designed with C++'s specifics in mind. It is your friend if any of the following problems is bothering you: * You are stuck with a sub-optimal design and wish you had done more prototyping before it was too late, but prototyping in C++ is by no means "rapid". * Your tests are slow as they depend on too many libraries or use expensive resources (e.g. a database). * Your tests are brittle as some resources they use are unreliable (e.g. the network). * You want to test how your code handles a failure (e.g. a file checksum error), but it's not easy to cause one. * You need to make sure that your module interacts with other modules in the right way, but it's hard to observe the interaction; therefore you resort to observing the side effects at the end of the action, which is awkward at best. * You want to "mock out" your dependencies, except that they don't have mock implementations yet; and, frankly, you aren't thrilled by some of those hand-written mocks. We encourage you to use Google Mock as: * a _design_ tool, for it lets you experiment with your interface design early and often. More iterations lead to better designs! * a _testing_ tool to cut your tests' outbound dependencies and probe the interaction between your module and its collaborators. # Getting Started # Using Google Mock is easy! Inside your C++ source file, just `#include` `"gtest/gtest.h"` and `"gmock/gmock.h"`, and you are ready to go. # A Case for Mock Turtles # Let's look at an example. Suppose you are developing a graphics program that relies on a LOGO-like API for drawing. How would you test that it does the right thing? Well, you can run it and compare the screen with a golden screen snapshot, but let's admit it: tests like this are expensive to run and fragile (What if you just upgraded to a shiny new graphics card that has better anti-aliasing? Suddenly you have to update all your golden images.). It would be too painful if all your tests are like this. Fortunately, you learned about Dependency Injection and know the right thing to do: instead of having your application talk to the drawing API directly, wrap the API in an interface (say, `Turtle`) and code to that interface: ```cpp class Turtle { ... virtual ~Turtle() {} virtual void PenUp() = 0; virtual void PenDown() = 0; virtual void Forward(int distance) = 0; virtual void Turn(int degrees) = 0; virtual void GoTo(int x, int y) = 0; virtual int GetX() const = 0; virtual int GetY() const = 0; }; ``` (Note that the destructor of `Turtle` **must** be virtual, as is the case for **all** classes you intend to inherit from - otherwise the destructor of the derived class will not be called when you delete an object through a base pointer, and you'll get corrupted program states like memory leaks.) You can control whether the turtle's movement will leave a trace using `PenUp()` and `PenDown()`, and control its movement using `Forward()`, `Turn()`, and `GoTo()`. Finally, `GetX()` and `GetY()` tell you the current position of the turtle. Your program will normally use a real implementation of this interface. In tests, you can use a mock implementation instead. This allows you to easily check what drawing primitives your program is calling, with what arguments, and in which order. Tests written this way are much more robust (they won't break because your new machine does anti-aliasing differently), easier to read and maintain (the intent of a test is expressed in the code, not in some binary images), and run _much, much faster_. # Writing the Mock Class # If you are lucky, the mocks you need to use have already been implemented by some nice people. If, however, you find yourself in the position to write a mock class, relax - Google Mock turns this task into a fun game! (Well, almost.) ## How to Define It ## Using the `Turtle` interface as example, here are the simple steps you need to follow: 1. Derive a class `MockTurtle` from `Turtle`. 1. Take a _virtual_ function of `Turtle` (while it's possible to [mock non-virtual methods using templates](cook_book.md#mocking-nonvirtual-methods), it's much more involved). Count how many arguments it has. 1. In the `public:` section of the child class, write `MOCK_METHODn();` (or `MOCK_CONST_METHODn();` if you are mocking a `const` method), where `n` is the number of the arguments; if you counted wrong, shame on you, and a compiler error will tell you so. 1. Now comes the fun part: you take the function signature, cut-and-paste the _function name_ as the _first_ argument to the macro, and leave what's left as the _second_ argument (in case you're curious, this is the _type of the function_). 1. Repeat until all virtual functions you want to mock are done. After the process, you should have something like: ```cpp #include "gmock/gmock.h" // Brings in Google Mock. class MockTurtle : public Turtle { public: ... MOCK_METHOD0(PenUp, void()); MOCK_METHOD0(PenDown, void()); MOCK_METHOD1(Forward, void(int distance)); MOCK_METHOD1(Turn, void(int degrees)); MOCK_METHOD2(GoTo, void(int x, int y)); MOCK_CONST_METHOD0(GetX, int()); MOCK_CONST_METHOD0(GetY, int()); }; ``` You don't need to define these mock methods somewhere else - the `MOCK_METHOD*` macros will generate the definitions for you. It's that simple! Once you get the hang of it, you can pump out mock classes faster than your source-control system can handle your check-ins. **Tip:** If even this is too much work for you, you'll find the `gmock_gen.py` tool in Google Mock's `scripts/generator/` directory (courtesy of the [cppclean](http://code.google.com/p/cppclean/) project) useful. This command-line tool requires that you have Python 2.4 installed. You give it a C++ file and the name of an abstract class defined in it, and it will print the definition of the mock class for you. Due to the complexity of the C++ language, this script may not always work, but it can be quite handy when it does. For more details, read the [user documentation](../scripts/generator/README). ## Where to Put It ## When you define a mock class, you need to decide where to put its definition. Some people put it in a `*_test.cc`. This is fine when the interface being mocked (say, `Foo`) is owned by the same person or team. Otherwise, when the owner of `Foo` changes it, your test could break. (You can't really expect `Foo`'s maintainer to fix every test that uses `Foo`, can you?) So, the rule of thumb is: if you need to mock `Foo` and it's owned by others, define the mock class in `Foo`'s package (better, in a `testing` sub-package such that you can clearly separate production code and testing utilities), and put it in a `mock_foo.h`. Then everyone can reference `mock_foo.h` from their tests. If `Foo` ever changes, there is only one copy of `MockFoo` to change, and only tests that depend on the changed methods need to be fixed. Another way to do it: you can introduce a thin layer `FooAdaptor` on top of `Foo` and code to this new interface. Since you own `FooAdaptor`, you can absorb changes in `Foo` much more easily. While this is more work initially, carefully choosing the adaptor interface can make your code easier to write and more readable (a net win in the long run), as you can choose `FooAdaptor` to fit your specific domain much better than `Foo` does. # Using Mocks in Tests # Once you have a mock class, using it is easy. The typical work flow is: 1. Import the Google Mock names from the `testing` namespace such that you can use them unqualified (You only have to do it once per file. Remember that namespaces are a good idea and good for your health.). 1. Create some mock objects. 1. Specify your expectations on them (How many times will a method be called? With what arguments? What should it do? etc.). 1. Exercise some code that uses the mocks; optionally, check the result using Google Test assertions. If a mock method is called more than expected or with wrong arguments, you'll get an error immediately. 1. When a mock is destructed, Google Mock will automatically check whether all expectations on it have been satisfied. Here's an example: ```cpp #include "path/to/mock-turtle.h" #include "gmock/gmock.h" #include "gtest/gtest.h" using ::testing::AtLeast; // #1 TEST(PainterTest, CanDrawSomething) { MockTurtle turtle; // #2 EXPECT_CALL(turtle, PenDown()) // #3 .Times(AtLeast(1)); Painter painter(&turtle); // #4 EXPECT_TRUE(painter.DrawCircle(0, 0, 10)); } // #5 int main(int argc, char** argv) { // The following line must be executed to initialize Google Mock // (and Google Test) before running the tests. ::testing::InitGoogleMock(&argc, argv); return RUN_ALL_TESTS(); } ``` As you might have guessed, this test checks that `PenDown()` is called at least once. If the `painter` object didn't call this method, your test will fail with a message like this: ``` path/to/my_test.cc:119: Failure Actual function call count doesn't match this expectation: Actually: never called; Expected: called at least once. ``` **Tip 1:** If you run the test from an Emacs buffer, you can hit `` on the line number displayed in the error message to jump right to the failed expectation. **Tip 2:** If your mock objects are never deleted, the final verification won't happen. Therefore it's a good idea to use a heap leak checker in your tests when you allocate mocks on the heap. **Important note:** Google Mock requires expectations to be set **before** the mock functions are called, otherwise the behavior is **undefined**. In particular, you mustn't interleave `EXPECT_CALL()`s and calls to the mock functions. This means `EXPECT_CALL()` should be read as expecting that a call will occur _in the future_, not that a call has occurred. Why does Google Mock work like that? Well, specifying the expectation beforehand allows Google Mock to report a violation as soon as it arises, when the context (stack trace, etc) is still available. This makes debugging much easier. Admittedly, this test is contrived and doesn't do much. You can easily achieve the same effect without using Google Mock. However, as we shall reveal soon, Google Mock allows you to do _much more_ with the mocks. ## Using Google Mock with Any Testing Framework ## If you want to use something other than Google Test (e.g. [CppUnit](http://sourceforge.net/projects/cppunit/) or [CxxTest](https://cxxtest.com/)) as your testing framework, just change the `main()` function in the previous section to: ```cpp int main(int argc, char** argv) { // The following line causes Google Mock to throw an exception on failure, // which will be interpreted by your testing framework as a test failure. ::testing::GTEST_FLAG(throw_on_failure) = true; ::testing::InitGoogleMock(&argc, argv); ... whatever your testing framework requires ... } ``` This approach has a catch: it makes Google Mock throw an exception from a mock object's destructor sometimes. With some compilers, this sometimes causes the test program to crash. You'll still be able to notice that the test has failed, but it's not a graceful failure. A better solution is to use Google Test's [event listener API](../../googletest/docs/advanced.md#extending-googletest-by-handling-test-events) to report a test failure to your testing framework properly. You'll need to implement the `OnTestPartResult()` method of the event listener interface, but it should be straightforward. If this turns out to be too much work, we suggest that you stick with Google Test, which works with Google Mock seamlessly (in fact, it is technically part of Google Mock.). If there is a reason that you cannot use Google Test, please let us know. # Setting Expectations # The key to using a mock object successfully is to set the _right expectations_ on it. If you set the expectations too strict, your test will fail as the result of unrelated changes. If you set them too loose, bugs can slip through. You want to do it just right such that your test can catch exactly the kind of bugs you intend it to catch. Google Mock provides the necessary means for you to do it "just right." ## General Syntax ## In Google Mock we use the `EXPECT_CALL()` macro to set an expectation on a mock method. The general syntax is: ```cpp EXPECT_CALL(mock_object, method(matchers)) .Times(cardinality) .WillOnce(action) .WillRepeatedly(action); ``` The macro has two arguments: first the mock object, and then the method and its arguments. Note that the two are separated by a comma (`,`), not a period (`.`). (Why using a comma? The answer is that it was necessary for technical reasons.) The macro can be followed by some optional _clauses_ that provide more information about the expectation. We'll discuss how each clause works in the coming sections. This syntax is designed to make an expectation read like English. For example, you can probably guess that ```cpp using ::testing::Return; ... EXPECT_CALL(turtle, GetX()) .Times(5) .WillOnce(Return(100)) .WillOnce(Return(150)) .WillRepeatedly(Return(200)); ``` says that the `turtle` object's `GetX()` method will be called five times, it will return 100 the first time, 150 the second time, and then 200 every time. Some people like to call this style of syntax a Domain-Specific Language (DSL). **Note:** Why do we use a macro to do this? It serves two purposes: first it makes expectations easily identifiable (either by `grep` or by a human reader), and second it allows Google Mock to include the source file location of a failed expectation in messages, making debugging easier. ## Matchers: What Arguments Do We Expect? ## When a mock function takes arguments, we must specify what arguments we are expecting; for example: ```cpp // Expects the turtle to move forward by 100 units. EXPECT_CALL(turtle, Forward(100)); ``` Sometimes you may not want to be too specific (Remember that talk about tests being too rigid? Over specification leads to brittle tests and obscures the intent of tests. Therefore we encourage you to specify only what's necessary - no more, no less.). If you care to check that `Forward()` will be called but aren't interested in its actual argument, write `_` as the argument, which means "anything goes": ```cpp using ::testing::_; ... // Expects the turtle to move forward. EXPECT_CALL(turtle, Forward(_)); ``` `_` is an instance of what we call **matchers**. A matcher is like a predicate and can test whether an argument is what we'd expect. You can use a matcher inside `EXPECT_CALL()` wherever a function argument is expected. -A list of built-in matchers can be found in the [CheatSheet](CheatSheet.md). For example, here's the `Ge` (greater than or equal) matcher: +A list of built-in matchers can be found in the [CheatSheet](cheat_sheet.md). For example, here's the `Ge` (greater than or equal) matcher: ```cpp using ::testing::Ge; ... EXPECT_CALL(turtle, Forward(Ge(100))); ``` This checks that the turtle will be told to go forward by at least 100 units. ## Cardinalities: How Many Times Will It Be Called? ## The first clause we can specify following an `EXPECT_CALL()` is `Times()`. We call its argument a **cardinality** as it tells _how many times_ the call should occur. It allows us to repeat an expectation many times without actually writing it as many times. More importantly, a cardinality can be "fuzzy", just like a matcher can be. This allows a user to express the intent of a test exactly. An interesting special case is when we say `Times(0)`. You may have guessed - it means that the function shouldn't be called with the given arguments at all, and Google Mock will report a Google Test failure whenever the function is (wrongfully) called. -We've seen `AtLeast(n)` as an example of fuzzy cardinalities earlier. For the list of built-in cardinalities you can use, see the [CheatSheet](CheatSheet.md). +We've seen `AtLeast(n)` as an example of fuzzy cardinalities earlier. For the list of built-in cardinalities you can use, see the [CheatSheet](cheat_sheet.md). The `Times()` clause can be omitted. **If you omit `Times()`, Google Mock will infer the cardinality for you.** The rules are easy to remember: * If **neither** `WillOnce()` **nor** `WillRepeatedly()` is in the `EXPECT_CALL()`, the inferred cardinality is `Times(1)`. * If there are `n WillOnce()`'s but **no** `WillRepeatedly()`, where `n` >= 1, the cardinality is `Times(n)`. * If there are `n WillOnce()`'s and **one** `WillRepeatedly()`, where `n` >= 0, the cardinality is `Times(AtLeast(n))`. **Quick quiz:** what do you think will happen if a function is expected to be called twice but actually called four times? ## Actions: What Should It Do? ## Remember that a mock object doesn't really have a working implementation? We as users have to tell it what to do when a method is invoked. This is easy in Google Mock. First, if the return type of a mock function is a built-in type or a pointer, the function has a **default action** (a `void` function will just return, a `bool` function will return `false`, and other functions will return 0). In addition, in C++ 11 and above, a mock function whose return type is default-constructible (i.e. has a default constructor) has a default action of returning a default-constructed value. If you don't say anything, this behavior will be used. Second, if a mock function doesn't have a default action, or the default action doesn't suit you, you can specify the action to be taken each time the expectation matches using a series of `WillOnce()` clauses followed by an optional `WillRepeatedly()`. For example, ```cpp using ::testing::Return; ... EXPECT_CALL(turtle, GetX()) .WillOnce(Return(100)) .WillOnce(Return(200)) .WillOnce(Return(300)); ``` This says that `turtle.GetX()` will be called _exactly three times_ (Google Mock inferred this from how many `WillOnce()` clauses we've written, since we didn't explicitly write `Times()`), and will return 100, 200, and 300 respectively. ```cpp using ::testing::Return; ... EXPECT_CALL(turtle, GetY()) .WillOnce(Return(100)) .WillOnce(Return(200)) .WillRepeatedly(Return(300)); ``` says that `turtle.GetY()` will be called _at least twice_ (Google Mock knows this as we've written two `WillOnce()` clauses and a `WillRepeatedly()` while having no explicit `Times()`), will return 100 the first time, 200 the second time, and 300 from the third time on. Of course, if you explicitly write a `Times()`, Google Mock will not try to infer the cardinality itself. What if the number you specified is larger than there are `WillOnce()` clauses? Well, after all `WillOnce()`s are used up, Google Mock will do the _default_ action for the function every time (unless, of course, you have a `WillRepeatedly()`.). -What can we do inside `WillOnce()` besides `Return()`? You can return a reference using `ReturnRef(variable)`, or invoke a pre-defined function, among [others](CheatSheet.md#actions). +What can we do inside `WillOnce()` besides `Return()`? You can return a reference using `ReturnRef(variable)`, or invoke a pre-defined function, among [others](cheat_sheet.md#actions). **Important note:** The `EXPECT_CALL()` statement evaluates the action clause only once, even though the action may be performed many times. Therefore you must be careful about side effects. The following may not do what you want: ```cpp int n = 100; EXPECT_CALL(turtle, GetX()) .Times(4) .WillRepeatedly(Return(n++)); ``` Instead of returning 100, 101, 102, ..., consecutively, this mock function will always return 100 as `n++` is only evaluated once. Similarly, `Return(new Foo)` will create a new `Foo` object when the `EXPECT_CALL()` is executed, and will return the same pointer every time. If you want the side effect to happen every time, you need to define a custom action, which we'll teach in the [CookBook](cook_book.md). Time for another quiz! What do you think the following means? ```cpp using ::testing::Return; ... EXPECT_CALL(turtle, GetY()) .Times(4) .WillOnce(Return(100)); ``` Obviously `turtle.GetY()` is expected to be called four times. But if you think it will return 100 every time, think twice! Remember that one `WillOnce()` clause will be consumed each time the function is invoked and the default action will be taken afterwards. So the right answer is that `turtle.GetY()` will return 100 the first time, but **return 0 from the second time on**, as returning 0 is the default action for `int` functions. ## Using Multiple Expectations ## So far we've only shown examples where you have a single expectation. More realistically, you're going to specify expectations on multiple mock methods, which may be from multiple mock objects. By default, when a mock method is invoked, Google Mock will search the expectations in the **reverse order** they are defined, and stop when an active expectation that matches the arguments is found (you can think of it as "newer rules override older ones."). If the matching expectation cannot take any more calls, you will get an upper-bound-violated failure. Here's an example: ```cpp using ::testing::_; ... EXPECT_CALL(turtle, Forward(_)); // #1 EXPECT_CALL(turtle, Forward(10)) // #2 .Times(2); ``` If `Forward(10)` is called three times in a row, the third time it will be an error, as the last matching expectation (#2) has been saturated. If, however, the third `Forward(10)` call is replaced by `Forward(20)`, then it would be OK, as now #1 will be the matching expectation. **Side note:** Why does Google Mock search for a match in the _reverse_ order of the expectations? The reason is that this allows a user to set up the default expectations in a mock object's constructor or the test fixture's set-up phase and then customize the mock by writing more specific expectations in the test body. So, if you have two expectations on the same method, you want to put the one with more specific matchers **after** the other, or the more specific rule would be shadowed by the more general one that comes after it. ## Ordered vs Unordered Calls ## By default, an expectation can match a call even though an earlier expectation hasn't been satisfied. In other words, the calls don't have to occur in the order the expectations are specified. Sometimes, you may want all the expected calls to occur in a strict order. To say this in Google Mock is easy: ```cpp using ::testing::InSequence; ... TEST(FooTest, DrawsLineSegment) { ... { InSequence dummy; EXPECT_CALL(turtle, PenDown()); EXPECT_CALL(turtle, Forward(100)); EXPECT_CALL(turtle, PenUp()); } Foo(); } ``` By creating an object of type `InSequence`, all expectations in its scope are put into a _sequence_ and have to occur _sequentially_. Since we are just relying on the constructor and destructor of this object to do the actual work, its name is really irrelevant. In this example, we test that `Foo()` calls the three expected functions in the order as written. If a call is made out-of-order, it will be an error. (What if you care about the relative order of some of the calls, but not all of them? Can you specify an arbitrary partial order? The answer is ... yes! If you are impatient, the details can be found in the [CookBook](cook_book.md#expecting-partially-ordered-calls).) ## All Expectations Are Sticky (Unless Said Otherwise) ## Now let's do a quick quiz to see how well you can use this mock stuff already. How would you test that the turtle is asked to go to the origin _exactly twice_ (you want to ignore any other instructions it receives)? After you've come up with your answer, take a look at ours and compare notes (solve it yourself first - don't cheat!): ```cpp using ::testing::_; ... EXPECT_CALL(turtle, GoTo(_, _)) // #1 .Times(AnyNumber()); EXPECT_CALL(turtle, GoTo(0, 0)) // #2 .Times(2); ``` Suppose `turtle.GoTo(0, 0)` is called three times. In the third time, Google Mock will see that the arguments match expectation #2 (remember that we always pick the last matching expectation). Now, since we said that there should be only two such calls, Google Mock will report an error immediately. This is basically what we've told you in the "Using Multiple Expectations" section above. This example shows that **expectations in Google Mock are "sticky" by default**, in the sense that they remain active even after we have reached their invocation upper bounds. This is an important rule to remember, as it affects the meaning of the spec, and is **different** to how it's done in many other mocking frameworks (Why'd we do that? Because we think our rule makes the common cases easier to express and understand.). Simple? Let's see if you've really understood it: what does the following code say? ```cpp using ::testing::Return; ... for (int i = n; i > 0; i--) { EXPECT_CALL(turtle, GetX()) .WillOnce(Return(10*i)); } ``` If you think it says that `turtle.GetX()` will be called `n` times and will return 10, 20, 30, ..., consecutively, think twice! The problem is that, as we said, expectations are sticky. So, the second time `turtle.GetX()` is called, the last (latest) `EXPECT_CALL()` statement will match, and will immediately lead to an "upper bound exceeded" error - this piece of code is not very useful! One correct way of saying that `turtle.GetX()` will return 10, 20, 30, ..., is to explicitly say that the expectations are _not_ sticky. In other words, they should _retire_ as soon as they are saturated: ```cpp using ::testing::Return; ... for (int i = n; i > 0; i--) { EXPECT_CALL(turtle, GetX()) .WillOnce(Return(10*i)) .RetiresOnSaturation(); } ``` And, there's a better way to do it: in this case, we expect the calls to occur in a specific order, and we line up the actions to match the order. Since the order is important here, we should make it explicit using a sequence: ```cpp using ::testing::InSequence; using ::testing::Return; ... { InSequence s; for (int i = 1; i <= n; i++) { EXPECT_CALL(turtle, GetX()) .WillOnce(Return(10*i)) .RetiresOnSaturation(); } } ``` By the way, the other situation where an expectation may _not_ be sticky is when it's in a sequence - as soon as another expectation that comes after it in the sequence has been used, it automatically retires (and will never be used to match any call). ## Uninteresting Calls ## A mock object may have many methods, and not all of them are that interesting. For example, in some tests we may not care about how many times `GetX()` and `GetY()` get called. In Google Mock, if you are not interested in a method, just don't say anything about it. If a call to this method occurs, you'll see a warning in the test output, but it won't be a failure. # What Now? # Congratulations! You've learned enough about Google Mock to start using it. Now, you might want to join the [googlemock](http://groups.google.com/group/googlemock) discussion group and actually write some tests using Google Mock - it will be fun. Hey, it may even be addictive - you've been warned. Then, if you feel like increasing your mock quotient, you should move on to the [CookBook](cook_book.md). You can learn many advanced features of Google Mock there -- and advance your level of enjoyment and testing bliss. diff --git a/googlemock/docs/FrequentlyAskedQuestions.md b/googlemock/docs/frequently_asked_questions.md similarity index 99% rename from googlemock/docs/FrequentlyAskedQuestions.md rename to googlemock/docs/frequently_asked_questions.md index 7b7ba0fb..de1ad2a2 100644 --- a/googlemock/docs/FrequentlyAskedQuestions.md +++ b/googlemock/docs/frequently_asked_questions.md @@ -1,556 +1,556 @@ Please send your questions to the [googlemock](http://groups.google.com/group/googlemock) discussion group. If you need help with compiler errors, make sure you have tried [Google Mock Doctor](#how-am-i-supposed-to-make-sense-of-these-horrible-template-errors) first. ## When I call a method on my mock object, the method for the real object is invoked instead. What's the problem? ## In order for a method to be mocked, it must be _virtual_, unless you use the [high-perf dependency injection technique](cook_book.md#mocking-nonvirtual-methods). ## I wrote some matchers. After I upgraded to a new version of Google Mock, they no longer compile. What's going on? ## After version 1.4.0 of Google Mock was released, we had an idea on how to make it easier to write matchers that can generate informative messages efficiently. We experimented with this idea and liked what we saw. Therefore we decided to implement it. Unfortunately, this means that if you have defined your own matchers by implementing `MatcherInterface` or using `MakePolymorphicMatcher()`, your definitions will no longer compile. Matchers defined using the `MATCHER*` family of macros are not affected. Sorry for the hassle if your matchers are affected. We believe it's in everyone's long-term interest to make this change sooner than later. Fortunately, it's usually not hard to migrate an existing matcher to the new API. Here's what you need to do: If you wrote your matcher like this: ```cpp // Old matcher definition that doesn't work with the latest // Google Mock. using ::testing::MatcherInterface; ... class MyWonderfulMatcher : public MatcherInterface { public: ... virtual bool Matches(MyType value) const { // Returns true if value matches. return value.GetFoo() > 5; } ... }; ``` you'll need to change it to: ```cpp // New matcher definition that works with the latest Google Mock. using ::testing::MatcherInterface; using ::testing::MatchResultListener; ... class MyWonderfulMatcher : public MatcherInterface { public: ... virtual bool MatchAndExplain(MyType value, MatchResultListener* listener) const { // Returns true if value matches. return value.GetFoo() > 5; } ... }; ``` (i.e. rename `Matches()` to `MatchAndExplain()` and give it a second argument of type `MatchResultListener*`.) If you were also using `ExplainMatchResultTo()` to improve the matcher message: ```cpp // Old matcher definition that doesn't work with the lastest // Google Mock. using ::testing::MatcherInterface; ... class MyWonderfulMatcher : public MatcherInterface { public: ... virtual bool Matches(MyType value) const { // Returns true if value matches. return value.GetFoo() > 5; } virtual void ExplainMatchResultTo(MyType value, ::std::ostream* os) const { // Prints some helpful information to os to help // a user understand why value matches (or doesn't match). *os << "the Foo property is " << value.GetFoo(); } ... }; ``` you should move the logic of `ExplainMatchResultTo()` into `MatchAndExplain()`, using the `MatchResultListener` argument where the `::std::ostream` was used: ```cpp // New matcher definition that works with the latest Google Mock. using ::testing::MatcherInterface; using ::testing::MatchResultListener; ... class MyWonderfulMatcher : public MatcherInterface { public: ... virtual bool MatchAndExplain(MyType value, MatchResultListener* listener) const { // Returns true if value matches. *listener << "the Foo property is " << value.GetFoo(); return value.GetFoo() > 5; } ... }; ``` If your matcher is defined using `MakePolymorphicMatcher()`: ```cpp // Old matcher definition that doesn't work with the latest // Google Mock. using ::testing::MakePolymorphicMatcher; ... class MyGreatMatcher { public: ... bool Matches(MyType value) const { // Returns true if value matches. return value.GetBar() < 42; } ... }; ... MakePolymorphicMatcher(MyGreatMatcher()) ... ``` you should rename the `Matches()` method to `MatchAndExplain()` and add a `MatchResultListener*` argument (the same as what you need to do for matchers defined by implementing `MatcherInterface`): ```cpp // New matcher definition that works with the latest Google Mock. using ::testing::MakePolymorphicMatcher; using ::testing::MatchResultListener; ... class MyGreatMatcher { public: ... bool MatchAndExplain(MyType value, MatchResultListener* listener) const { // Returns true if value matches. return value.GetBar() < 42; } ... }; ... MakePolymorphicMatcher(MyGreatMatcher()) ... ``` If your polymorphic matcher uses `ExplainMatchResultTo()` for better failure messages: ```cpp // Old matcher definition that doesn't work with the latest // Google Mock. using ::testing::MakePolymorphicMatcher; ... class MyGreatMatcher { public: ... bool Matches(MyType value) const { // Returns true if value matches. return value.GetBar() < 42; } ... }; void ExplainMatchResultTo(const MyGreatMatcher& matcher, MyType value, ::std::ostream* os) { // Prints some helpful information to os to help // a user understand why value matches (or doesn't match). *os << "the Bar property is " << value.GetBar(); } ... MakePolymorphicMatcher(MyGreatMatcher()) ... ``` you'll need to move the logic inside `ExplainMatchResultTo()` to `MatchAndExplain()`: ```cpp // New matcher definition that works with the latest Google Mock. using ::testing::MakePolymorphicMatcher; using ::testing::MatchResultListener; ... class MyGreatMatcher { public: ... bool MatchAndExplain(MyType value, MatchResultListener* listener) const { // Returns true if value matches. *listener << "the Bar property is " << value.GetBar(); return value.GetBar() < 42; } ... }; ... MakePolymorphicMatcher(MyGreatMatcher()) ... ``` For more information, you can read these [two](cook_book.md#writing-new-monomorphic-matchers) [recipes](cook_book.md#writing-new-polymorphic-matchers) from the cookbook. As always, you are welcome to post questions on `googlemock@googlegroups.com` if you need any help. ## When using Google Mock, do I have to use Google Test as the testing framework? I have my favorite testing framework and don't want to switch. ## Google Mock works out of the box with Google Test. However, it's easy to configure it to work with any testing framework of your choice. -[Here](ForDummies.md#using-google-mock-with-any-testing-framework) is how. +[Here](for_dummies.md#using-google-mock-with-any-testing-framework) is how. ## How am I supposed to make sense of these horrible template errors? ## If you are confused by the compiler errors gcc threw at you, try consulting the _Google Mock Doctor_ tool first. What it does is to scan stdin for gcc error messages, and spit out diagnoses on the problems (we call them diseases) your code has. To "install", run command: ``` alias gmd='/scripts/gmock_doctor.py' ``` To use it, do: ``` 2>&1 | gmd ``` For example: ``` make my_test 2>&1 | gmd ``` Or you can run `gmd` and copy-n-paste gcc's error messages to it. ## Can I mock a variadic function? ## You cannot mock a variadic function (i.e. a function taking ellipsis (`...`) arguments) directly in Google Mock. The problem is that in general, there is _no way_ for a mock object to know how many arguments are passed to the variadic method, and what the arguments' types are. Only the _author of the base class_ knows the protocol, and we cannot look into their head. Therefore, to mock such a function, the _user_ must teach the mock object how to figure out the number of arguments and their types. One way to do it is to provide overloaded versions of the function. Ellipsis arguments are inherited from C and not really a C++ feature. They are unsafe to use and don't work with arguments that have constructors or destructors. Therefore we recommend to avoid them in C++ as much as possible. ## I have a failed test where Google Mock tells me TWICE that a particular expectation is not satisfied. Isn't this redundant? ## When Google Mock detects a failure, it prints relevant information (the mock function arguments, the state of relevant expectations, and etc) to help the user debug. If another failure is detected, Google Mock will do the same, including printing the state of relevant expectations. Sometimes an expectation's state didn't change between two failures, and you'll see the same description of the state twice. They are however _not_ redundant, as they refer to _different points in time_. The fact they are the same _is_ interesting information. ## I get a heap check failure when using a mock object, but using a real object is fine. What can be wrong? ## Does the class (hopefully a pure interface) you are mocking have a virtual destructor? Whenever you derive from a base class, make sure its destructor is virtual. Otherwise Bad Things will happen. Consider the following code: ```cpp class Base { public: // Not virtual, but should be. ~Base() { ... } ... }; class Derived : public Base { public: ... private: std::string value_; }; ... Base* p = new Derived; ... delete p; // Surprise! ~Base() will be called, but ~Derived() will not // - value_ is leaked. ``` By changing `~Base()` to virtual, `~Derived()` will be correctly called when `delete p` is executed, and the heap checker will be happy. ## The "newer expectations override older ones" rule makes writing expectations awkward. Why does Google Mock do that? ## When people complain about this, often they are referring to code like: ```cpp // foo.Bar() should be called twice, return 1 the first time, and return // 2 the second time. However, I have to write the expectations in the // reverse order. This sucks big time!!! EXPECT_CALL(foo, Bar()) .WillOnce(Return(2)) .RetiresOnSaturation(); EXPECT_CALL(foo, Bar()) .WillOnce(Return(1)) .RetiresOnSaturation(); ``` The problem is that they didn't pick the **best** way to express the test's intent. By default, expectations don't have to be matched in _any_ particular order. If you want them to match in a certain order, you need to be explicit. This is Google Mock's (and jMock's) fundamental philosophy: it's easy to accidentally over-specify your tests, and we want to make it harder to do so. There are two better ways to write the test spec. You could either put the expectations in sequence: ```cpp // foo.Bar() should be called twice, return 1 the first time, and return // 2 the second time. Using a sequence, we can write the expectations // in their natural order. { InSequence s; EXPECT_CALL(foo, Bar()) .WillOnce(Return(1)) .RetiresOnSaturation(); EXPECT_CALL(foo, Bar()) .WillOnce(Return(2)) .RetiresOnSaturation(); } ``` or you can put the sequence of actions in the same expectation: ```cpp // foo.Bar() should be called twice, return 1 the first time, and return // 2 the second time. EXPECT_CALL(foo, Bar()) .WillOnce(Return(1)) .WillOnce(Return(2)) .RetiresOnSaturation(); ``` Back to the original questions: why does Google Mock search the expectations (and `ON_CALL`s) from back to front? Because this allows a user to set up a mock's behavior for the common case early (e.g. in the mock's constructor or the test fixture's set-up phase) and customize it with more specific rules later. If Google Mock searches from front to back, this very useful pattern won't be possible. ## Google Mock prints a warning when a function without EXPECT\_CALL is called, even if I have set its behavior using ON\_CALL. Would it be reasonable not to show the warning in this case? ## When choosing between being neat and being safe, we lean toward the latter. So the answer is that we think it's better to show the warning. Often people write `ON_CALL`s in the mock object's constructor or `SetUp()`, as the default behavior rarely changes from test to test. Then in the test body they set the expectations, which are often different for each test. Having an `ON_CALL` in the set-up part of a test doesn't mean that the calls are expected. If there's no `EXPECT_CALL` and the method is called, it's possibly an error. If we quietly let the call go through without notifying the user, bugs may creep in unnoticed. If, however, you are sure that the calls are OK, you can write ```cpp EXPECT_CALL(foo, Bar(_)) .WillRepeatedly(...); ``` instead of ```cpp ON_CALL(foo, Bar(_)) .WillByDefault(...); ``` This tells Google Mock that you do expect the calls and no warning should be printed. Also, you can control the verbosity using the `--gmock_verbose` flag. If you find the output too noisy when debugging, just choose a less verbose level. ## How can I delete the mock function's argument in an action? ## If you find yourself needing to perform some action that's not supported by Google Mock directly, remember that you can define your own actions using [MakeAction()](cook_book.md#writing-new-actions-quickly) or [MakePolymorphicAction()](cook_book.md#writing-new-polymorphic-actions), or you can write a stub function and invoke it using [Invoke()](cook_book.md#using-functionsmethodsfunctors-as-actions). ## MOCK\_METHODn()'s second argument looks funny. Why don't you use the MOCK\_METHODn(Method, return\_type, arg\_1, ..., arg\_n) syntax? ## What?! I think it's beautiful. :-) While which syntax looks more natural is a subjective matter to some extent, Google Mock's syntax was chosen for several practical advantages it has. Try to mock a function that takes a map as an argument: ```cpp virtual int GetSize(const map& m); ``` Using the proposed syntax, it would be: ```cpp MOCK_METHOD1(GetSize, int, const map& m); ``` Guess what? You'll get a compiler error as the compiler thinks that `const map& m` are **two**, not one, arguments. To work around this you can use `typedef` to give the map type a name, but that gets in the way of your work. Google Mock's syntax avoids this problem as the function's argument types are protected inside a pair of parentheses: ```cpp // This compiles fine. MOCK_METHOD1(GetSize, int(const map& m)); ``` You still need a `typedef` if the return type contains an unprotected comma, but that's much rarer. Other advantages include: 1. `MOCK_METHOD1(Foo, int, bool)` can leave a reader wonder whether the method returns `int` or `bool`, while there won't be such confusion using Google Mock's syntax. 1. The way Google Mock describes a function type is nothing new, although many people may not be familiar with it. The same syntax was used in C, and the `function` library in `tr1` uses this syntax extensively. Since `tr1` will become a part of the new version of STL, we feel very comfortable to be consistent with it. 1. The function type syntax is also used in other parts of Google Mock's API (e.g. the action interface) in order to make the implementation tractable. A user needs to learn it anyway in order to utilize Google Mock's more advanced features. We'd as well stick to the same syntax in `MOCK_METHOD*`! ## My code calls a static/global function. Can I mock it? ## You can, but you need to make some changes. In general, if you find yourself needing to mock a static function, it's a sign that your modules are too tightly coupled (and less flexible, less reusable, less testable, etc). You are probably better off defining a small interface and call the function through that interface, which then can be easily mocked. It's a bit of work initially, but usually pays for itself quickly. This Google Testing Blog [post](https://testing.googleblog.com/2008/06/defeat-static-cling.html) says it excellently. Check it out. ## My mock object needs to do complex stuff. It's a lot of pain to specify the actions. Google Mock sucks! ## I know it's not a question, but you get an answer for free any way. :-) With Google Mock, you can create mocks in C++ easily. And people might be tempted to use them everywhere. Sometimes they work great, and sometimes you may find them, well, a pain to use. So, what's wrong in the latter case? When you write a test without using mocks, you exercise the code and assert that it returns the correct value or that the system is in an expected state. This is sometimes called "state-based testing". Mocks are great for what some call "interaction-based" testing: instead of checking the system state at the very end, mock objects verify that they are invoked the right way and report an error as soon as it arises, giving you a handle on the precise context in which the error was triggered. This is often more effective and economical to do than state-based testing. If you are doing state-based testing and using a test double just to simulate the real object, you are probably better off using a fake. Using a mock in this case causes pain, as it's not a strong point for mocks to perform complex actions. If you experience this and think that mocks suck, you are just not using the right tool for your problem. Or, you might be trying to solve the wrong problem. :-) ## I got a warning "Uninteresting function call encountered - default action taken.." Should I panic? ## By all means, NO! It's just an FYI. What it means is that you have a mock function, you haven't set any expectations on it (by Google Mock's rule this means that you are not interested in calls to this function and therefore it can be called any number of times), and it is called. That's OK - you didn't say it's not OK to call the function! What if you actually meant to disallow this function to be called, but forgot to write `EXPECT_CALL(foo, Bar()).Times(0)`? While one can argue that it's the user's fault, Google Mock tries to be nice and prints you a note. So, when you see the message and believe that there shouldn't be any uninteresting calls, you should investigate what's going on. To make your life easier, Google Mock prints the function name and arguments when an uninteresting call is encountered. ## I want to define a custom action. Should I use Invoke() or implement the action interface? ## Either way is fine - you want to choose the one that's more convenient for your circumstance. Usually, if your action is for a particular function type, defining it using `Invoke()` should be easier; if your action can be used in functions of different types (e.g. if you are defining `Return(value)`), `MakePolymorphicAction()` is easiest. Sometimes you want precise control on what types of functions the action can be used in, and implementing `ActionInterface` is the way to go here. See the implementation of `Return()` in `include/gmock/gmock-actions.h` for an example. ## I'm using the set-argument-pointee action, and the compiler complains about "conflicting return type specified". What does it mean? ## You got this error as Google Mock has no idea what value it should return when the mock method is called. `SetArgPointee()` says what the side effect is, but doesn't say what the return value should be. You need `DoAll()` to chain a `SetArgPointee()` with a `Return()`. See this [recipe](cook_book.md#mocking-side-effects) for more details and an example. ## My question is not in your FAQ! ## If you cannot find the answer to your question in this FAQ, there are some other resources you can use: 1. search the mailing list [archive](http://groups.google.com/group/googlemock/topics), 1. ask it on [googlemock@googlegroups.com](mailto:googlemock@googlegroups.com) and someone will answer it (to prevent spam, we require you to join the [discussion group](http://groups.google.com/group/googlemock) before you can post.). Please note that creating an issue in the [issue tracker](https://github.com/google/googletest/issues) is _not_ a good way to get your answer, as it is monitored infrequently by a very small number of people. When asking a question, it's helpful to provide as much of the following information as possible (people cannot help you if there's not enough information in your question): * the version (or the revision number if you check out from SVN directly) of Google Mock you use (Google Mock is under active development, so it's possible that your problem has been solved in a later version), * your operating system, * the name and version of your compiler, * the complete command line flags you give to your compiler, * the complete compiler error messages (if the question is about compilation), * the _actual_ code (ideally, a minimal but complete program) that has the problem you encounter. diff --git a/googlemock/docs/KnownIssues.md b/googlemock/docs/known_issues.md similarity index 100% rename from googlemock/docs/KnownIssues.md rename to googlemock/docs/known_issues.md diff --git a/googletest/docs/advanced.md b/googletest/docs/advanced.md index 603777c1..d0f1bfab 100644 --- a/googletest/docs/advanced.md +++ b/googletest/docs/advanced.md @@ -1,2588 +1,2588 @@ # Advanced googletest Topics ## Introduction Now that you have read the [googletest Primer](primer.md) and learned how to write tests using googletest, it's time to learn some new tricks. This document will show you more assertions as well as how to construct complex failure messages, propagate fatal failures, reuse and speed up your test fixtures, and use various flags with your tests. ## More Assertions This section covers some less frequently used, but still significant, assertions. ### Explicit Success and Failure These three assertions do not actually test a value or expression. Instead, they generate a success or failure directly. Like the macros that actually perform a test, you may stream a custom failure message into them. ```c++ SUCCEED(); ``` Generates a success. This does **NOT** make the overall test succeed. A test is considered successful only if none of its assertions fail during its execution. NOTE: `SUCCEED()` is purely documentary and currently doesn't generate any user-visible output. However, we may add `SUCCEED()` messages to googletest's output in the future. ```c++ FAIL(); ADD_FAILURE(); ADD_FAILURE_AT("file_path", line_number); ``` `FAIL()` generates a fatal failure, while `ADD_FAILURE()` and `ADD_FAILURE_AT()` generate a nonfatal failure. These are useful when control flow, rather than a Boolean expression, determines the test's success or failure. For example, you might want to write something like: ```c++ switch(expression) { case 1: ... some checks ... case 2: ... some other checks ... default: FAIL() << "We shouldn't get here."; } ``` NOTE: you can only use `FAIL()` in functions that return `void`. See the [Assertion Placement section](#assertion-placement) for more information. **Availability**: Linux, Windows, Mac. ### Exception Assertions These are for verifying that a piece of code throws (or does not throw) an exception of the given type: Fatal assertion | Nonfatal assertion | Verifies ------------------------------------------ | ------------------------------------------ | -------- `ASSERT_THROW(statement, exception_type);` | `EXPECT_THROW(statement, exception_type);` | `statement` throws an exception of the given type `ASSERT_ANY_THROW(statement);` | `EXPECT_ANY_THROW(statement);` | `statement` throws an exception of any type `ASSERT_NO_THROW(statement);` | `EXPECT_NO_THROW(statement);` | `statement` doesn't throw any exception Examples: ```c++ ASSERT_THROW(Foo(5), bar_exception); EXPECT_NO_THROW({ int n = 5; Bar(&n); }); ``` **Availability**: Linux, Windows, Mac; requires exceptions to be enabled in the build environment (note that `google3` **disables** exceptions). ### Predicate Assertions for Better Error Messages Even though googletest has a rich set of assertions, they can never be complete, as it's impossible (nor a good idea) to anticipate all scenarios a user might run into. Therefore, sometimes a user has to use `EXPECT_TRUE()` to check a complex expression, for lack of a better macro. This has the problem of not showing you the values of the parts of the expression, making it hard to understand what went wrong. As a workaround, some users choose to construct the failure message by themselves, streaming it into `EXPECT_TRUE()`. However, this is awkward especially when the expression has side-effects or is expensive to evaluate. googletest gives you three different options to solve this problem: #### Using an Existing Boolean Function If you already have a function or functor that returns `bool` (or a type that can be implicitly converted to `bool`), you can use it in a *predicate assertion* to get the function arguments printed for free: | Fatal assertion | Nonfatal assertion | Verifies | | -------------------- | -------------------- | --------------------------- | | `ASSERT_PRED1(pred1, | `EXPECT_PRED1(pred1, | `pred1(val1)` is true | : val1);` : val1);` : : | `ASSERT_PRED2(pred2, | `EXPECT_PRED2(pred2, | `pred2(val1, val2)` is true | : val1, val2);` : val1, val2);` : : | `...` | `...` | ... | In the above, `predn` is an `n`-ary predicate function or functor, where `val1`, `val2`, ..., and `valn` are its arguments. The assertion succeeds if the predicate returns `true` when applied to the given arguments, and fails otherwise. When the assertion fails, it prints the value of each argument. In either case, the arguments are evaluated exactly once. Here's an example. Given ```c++ // Returns true if m and n have no common divisors except 1. bool MutuallyPrime(int m, int n) { ... } const int a = 3; const int b = 4; const int c = 10; ``` the assertion ```c++ EXPECT_PRED2(MutuallyPrime, a, b); ``` will succeed, while the assertion ```c++ EXPECT_PRED2(MutuallyPrime, b, c); ``` will fail with the message ```none MutuallyPrime(b, c) is false, where b is 4 c is 10 ``` > NOTE: > > 1. If you see a compiler error "no matching function to call" when using > `ASSERT_PRED*` or `EXPECT_PRED*`, please see > [this](faq.md#the-compiler-complains-no-matching-function-to-call-when-i-use-assert_pred-how-do-i-fix-it) for how to resolve it. > 1. Currently we only provide predicate assertions of arity <= 5. If you need > a higher-arity assertion, let [us](https://github.com/google/googletest/issues) know. **Availability**: Linux, Windows, Mac. #### Using a Function That Returns an AssertionResult While `EXPECT_PRED*()` and friends are handy for a quick job, the syntax is not satisfactory: you have to use different macros for different arities, and it feels more like Lisp than C++. The `::testing::AssertionResult` class solves this problem. An `AssertionResult` object represents the result of an assertion (whether it's a success or a failure, and an associated message). You can create an `AssertionResult` using one of these factory functions: ```c++ namespace testing { // Returns an AssertionResult object to indicate that an assertion has // succeeded. AssertionResult AssertionSuccess(); // Returns an AssertionResult object to indicate that an assertion has // failed. AssertionResult AssertionFailure(); } ``` You can then use the `<<` operator to stream messages to the `AssertionResult` object. To provide more readable messages in Boolean assertions (e.g. `EXPECT_TRUE()`), write a predicate function that returns `AssertionResult` instead of `bool`. For example, if you define `IsEven()` as: ```c++ ::testing::AssertionResult IsEven(int n) { if ((n % 2) == 0) return ::testing::AssertionSuccess(); else return ::testing::AssertionFailure() << n << " is odd"; } ``` instead of: ```c++ bool IsEven(int n) { return (n % 2) == 0; } ``` the failed assertion `EXPECT_TRUE(IsEven(Fib(4)))` will print: ```none Value of: IsEven(Fib(4)) Actual: false (3 is odd) Expected: true ``` instead of a more opaque ```none Value of: IsEven(Fib(4)) Actual: false Expected: true ``` If you want informative messages in `EXPECT_FALSE` and `ASSERT_FALSE` as well (one third of Boolean assertions in the Google code base are negative ones), and are fine with making the predicate slower in the success case, you can supply a success message: ```c++ ::testing::AssertionResult IsEven(int n) { if ((n % 2) == 0) return ::testing::AssertionSuccess() << n << " is even"; else return ::testing::AssertionFailure() << n << " is odd"; } ``` Then the statement `EXPECT_FALSE(IsEven(Fib(6)))` will print ```none Value of: IsEven(Fib(6)) Actual: true (8 is even) Expected: false ``` **Availability**: Linux, Windows, Mac. #### Using a Predicate-Formatter If you find the default message generated by `(ASSERT|EXPECT)_PRED*` and `(ASSERT|EXPECT)_(TRUE|FALSE)` unsatisfactory, or some arguments to your predicate do not support streaming to `ostream`, you can instead use the following *predicate-formatter assertions* to *fully* customize how the message is formatted: Fatal assertion | Nonfatal assertion | Verifies ------------------------------------------------ | ------------------------------------------------ | -------- `ASSERT_PRED_FORMAT1(pred_format1, val1);` | `EXPECT_PRED_FORMAT1(pred_format1, val1);` | `pred_format1(val1)` is successful `ASSERT_PRED_FORMAT2(pred_format2, val1, val2);` | `EXPECT_PRED_FORMAT2(pred_format2, val1, val2);` | `pred_format2(val1, val2)` is successful `...` | `...` | ... The difference between this and the previous group of macros is that instead of a predicate, `(ASSERT|EXPECT)_PRED_FORMAT*` take a *predicate-formatter* (`pred_formatn`), which is a function or functor with the signature: ```c++ ::testing::AssertionResult PredicateFormattern(const char* expr1, const char* expr2, ... const char* exprn, T1 val1, T2 val2, ... Tn valn); ``` where `val1`, `val2`, ..., and `valn` are the values of the predicate arguments, and `expr1`, `expr2`, ..., and `exprn` are the corresponding expressions as they appear in the source code. The types `T1`, `T2`, ..., and `Tn` can be either value types or reference types. For example, if an argument has type `Foo`, you can declare it as either `Foo` or `const Foo&`, whichever is appropriate. As an example, let's improve the failure message in `MutuallyPrime()`, which was used with `EXPECT_PRED2()`: ```c++ // Returns the smallest prime common divisor of m and n, // or 1 when m and n are mutually prime. int SmallestPrimeCommonDivisor(int m, int n) { ... } // A predicate-formatter for asserting that two integers are mutually prime. ::testing::AssertionResult AssertMutuallyPrime(const char* m_expr, const char* n_expr, int m, int n) { if (MutuallyPrime(m, n)) return ::testing::AssertionSuccess(); return ::testing::AssertionFailure() << m_expr << " and " << n_expr << " (" << m << " and " << n << ") are not mutually prime, " << "as they have a common divisor " << SmallestPrimeCommonDivisor(m, n); } ``` With this predicate-formatter, we can use ```c++ EXPECT_PRED_FORMAT2(AssertMutuallyPrime, b, c); ``` to generate the message ```none b and c (4 and 10) are not mutually prime, as they have a common divisor 2. ``` As you may have realized, many of the built-in assertions we introduced earlier are special cases of `(EXPECT|ASSERT)_PRED_FORMAT*`. In fact, most of them are indeed defined using `(EXPECT|ASSERT)_PRED_FORMAT*`. **Availability**: Linux, Windows, Mac. ### Floating-Point Comparison Comparing floating-point numbers is tricky. Due to round-off errors, it is very unlikely that two floating-points will match exactly. Therefore, `ASSERT_EQ` 's naive comparison usually doesn't work. And since floating-points can have a wide value range, no single fixed error bound works. It's better to compare by a fixed relative error bound, except for values close to 0 due to the loss of precision there. In general, for floating-point comparison to make sense, the user needs to carefully choose the error bound. If they don't want or care to, comparing in terms of Units in the Last Place (ULPs) is a good default, and googletest provides assertions to do this. Full details about ULPs are quite long; if you want to learn more, see [here](https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/). #### Floating-Point Macros | Fatal assertion | Nonfatal assertion | Verifies | | ----------------------- | ----------------------- | ----------------------- | | `ASSERT_FLOAT_EQ(val1, | `EXPECT_FLOAT_EQ(val1, | the two `float` values | : val2);` : val2);` : are almost equal : | `ASSERT_DOUBLE_EQ(val1, | `EXPECT_DOUBLE_EQ(val1, | the two `double` values | : val2);` : val2);` : are almost equal : By "almost equal" we mean the values are within 4 ULP's from each other. The following assertions allow you to choose the acceptable error bound: | Fatal assertion | Nonfatal assertion | Verifies | | ------------------ | ------------------------ | ------------------------- | | `ASSERT_NEAR(val1, | `EXPECT_NEAR(val1, val2, | the difference between | : val2, abs_error);` : abs_error);` : `val1` and `val2` doesn't : : : : exceed the given absolute : : : : error : **Availability**: Linux, Windows, Mac. #### Floating-Point Predicate-Format Functions Some floating-point operations are useful, but not that often used. In order to avoid an explosion of new macros, we provide them as predicate-format functions that can be used in predicate assertion macros (e.g. `EXPECT_PRED_FORMAT2`, etc). ```c++ EXPECT_PRED_FORMAT2(::testing::FloatLE, val1, val2); EXPECT_PRED_FORMAT2(::testing::DoubleLE, val1, val2); ``` Verifies that `val1` is less than, or almost equal to, `val2`. You can replace `EXPECT_PRED_FORMAT2` in the above table with `ASSERT_PRED_FORMAT2`. **Availability**: Linux, Windows, Mac. ### Asserting Using gMock Matchers Google-developed C++ mocking framework [gMock](../../googlemock) comes with a library of matchers for validating arguments passed to mock objects. A gMock *matcher* is basically a predicate that knows how to describe itself. It can be used in these assertion macros: | Fatal assertion | Nonfatal assertion | Verifies | | ------------------------------ | ------------------------------ | --------------------- | | `ASSERT_THAT(value, matcher);` | `EXPECT_THAT(value, matcher);` | value matches matcher | For example, `StartsWith(prefix)` is a matcher that matches a string starting with `prefix`, and you can write: ```c++ using ::testing::StartsWith; ... // Verifies that Foo() returns a string starting with "Hello". EXPECT_THAT(Foo(), StartsWith("Hello")); ``` Read this [recipe](../../googlemock/docs/cook_book.md#using-matchers-in-google-test-assertions) in the gMock Cookbook for more details. gMock has a rich set of matchers. You can do many things googletest cannot do alone with them. For a list of matchers gMock provides, read [this](../../googlemock/docs/cook_book.md#using-matchers). Especially useful among them are some [protocol buffer matchers](https://github.com/google/nucleus/blob/master/nucleus/testing/protocol-buffer-matchers.h). It's easy to write your [own matchers](../../googlemock/docs/cook_book.md#writing-new-matchers-quickly) too. For example, you can use gMock's [EqualsProto](https://github.com/google/nucleus/blob/master/nucleus/testing/protocol-buffer-matchers.h) to compare protos in your tests: ```c++ #include "testing/base/public/gmock.h" using ::testing::EqualsProto; ... EXPECT_THAT(actual_proto, EqualsProto("foo: 123 bar: 'xyz'")); EXPECT_THAT(*actual_proto_ptr, EqualsProto(expected_proto)); ``` gMock is bundled with googletest, so you don't need to add any build dependency in order to take advantage of this. Just include `"testing/base/public/gmock.h"` and you're ready to go. **Availability**: Linux, Windows, and Mac. ### More String Assertions (Please read the [previous](#asserting-using-gmock-matchers) section first if you haven't.) -You can use the gMock [string matchers](../../googlemock/docs/CheatSheet.md#string-matchers) +You can use the gMock [string matchers](../../googlemock/docs/cheat_sheet.md#string-matchers) with `EXPECT_THAT()` or `ASSERT_THAT()` to do more string comparison tricks (sub-string, prefix, suffix, regular expression, and etc). For example, ```c++ using ::testing::HasSubstr; using ::testing::MatchesRegex; ... ASSERT_THAT(foo_string, HasSubstr("needle")); EXPECT_THAT(bar_string, MatchesRegex("\\w*\\d+")); ``` **Availability**: Linux, Windows, Mac. If the string contains a well-formed HTML or XML document, you can check whether its DOM tree matches an [XPath expression](http://www.w3.org/TR/xpath/#contents): ```c++ // Currently still in //template/prototemplate/testing:xpath_matcher #include "template/prototemplate/testing/xpath_matcher.h" using prototemplate::testing::MatchesXPath; EXPECT_THAT(html_string, MatchesXPath("//a[text()='click here']")); ``` **Availability**: Linux. ### Windows HRESULT assertions These assertions test for `HRESULT` success or failure. Fatal assertion | Nonfatal assertion | Verifies -------------------------------------- | -------------------------------------- | -------- `ASSERT_HRESULT_SUCCEEDED(expression)` | `EXPECT_HRESULT_SUCCEEDED(expression)` | `expression` is a success `HRESULT` `ASSERT_HRESULT_FAILED(expression)` | `EXPECT_HRESULT_FAILED(expression)` | `expression` is a failure `HRESULT` The generated output contains the human-readable error message associated with the `HRESULT` code returned by `expression`. You might use them like this: ```c++ CComPtr shell; ASSERT_HRESULT_SUCCEEDED(shell.CoCreateInstance(L"Shell.Application")); CComVariant empty; ASSERT_HRESULT_SUCCEEDED(shell->ShellExecute(CComBSTR(url), empty, empty, empty, empty)); ``` **Availability**: Windows. ### Type Assertions You can call the function ```c++ ::testing::StaticAssertTypeEq(); ``` to assert that types `T1` and `T2` are the same. The function does nothing if the assertion is satisfied. If the types are different, the function call will fail to compile, and the compiler error message will likely (depending on the compiler) show you the actual values of `T1` and `T2`. This is mainly useful inside template code. **Caveat**: When used inside a member function of a class template or a function template, `StaticAssertTypeEq()` is effective only if the function is instantiated. For example, given: ```c++ template class Foo { public: void Bar() { ::testing::StaticAssertTypeEq(); } }; ``` the code: ```c++ void Test1() { Foo foo; } ``` will not generate a compiler error, as `Foo::Bar()` is never actually instantiated. Instead, you need: ```c++ void Test2() { Foo foo; foo.Bar(); } ``` to cause a compiler error. **Availability**: Linux, Windows, Mac. ### Assertion Placement You can use assertions in any C++ function. In particular, it doesn't have to be a method of the test fixture class. The one constraint is that assertions that generate a fatal failure (`FAIL*` and `ASSERT_*`) can only be used in void-returning functions. This is a consequence of Google's not using exceptions. By placing it in a non-void function you'll get a confusing compile error like `"error: void value not ignored as it ought to be"` or `"cannot initialize return object of type 'bool' with an rvalue of type 'void'"` or `"error: no viable conversion from 'void' to 'string'"`. If you need to use fatal assertions in a function that returns non-void, one option is to make the function return the value in an out parameter instead. For example, you can rewrite `T2 Foo(T1 x)` to `void Foo(T1 x, T2* result)`. You need to make sure that `*result` contains some sensible value even when the function returns prematurely. As the function now returns `void`, you can use any assertion inside of it. If changing the function's type is not an option, you should just use assertions that generate non-fatal failures, such as `ADD_FAILURE*` and `EXPECT_*`. NOTE: Constructors and destructors are not considered void-returning functions, according to the C++ language specification, and so you may not use fatal assertions in them. You'll get a compilation error if you try. A simple workaround is to transfer the entire body of the constructor or destructor to a private void-returning method. However, you should be aware that a fatal assertion failure in a constructor does not terminate the current test, as your intuition might suggest; it merely returns from the constructor early, possibly leaving your object in a partially-constructed state. Likewise, a fatal assertion failure in a destructor may leave your object in a partially-destructed state. Use assertions carefully in these situations! ## Teaching googletest How to Print Your Values When a test assertion such as `EXPECT_EQ` fails, googletest prints the argument values to help you debug. It does this using a user-extensible value printer. This printer knows how to print built-in C++ types, native arrays, STL containers, and any type that supports the `<<` operator. For other types, it prints the raw bytes in the value and hopes that you the user can figure it out. As mentioned earlier, the printer is *extensible*. That means you can teach it to do a better job at printing your particular type than to dump the bytes. To do that, define `<<` for your type: ```c++ // Streams are allowed only for logging. Don't include this for // any other purpose. #include namespace foo { class Bar { // We want googletest to be able to print instances of this. ... // Create a free inline friend function. friend std::ostream& operator<<(std::ostream& os, const Bar& bar) { return os << bar.DebugString(); // whatever needed to print bar to os } }; // If you can't declare the function in the class it's important that the // << operator is defined in the SAME namespace that defines Bar. C++'s look-up // rules rely on that. std::ostream& operator<<(std::ostream& os, const Bar& bar) { return os << bar.DebugString(); // whatever needed to print bar to os } } // namespace foo ``` Sometimes, this might not be an option: your team may consider it bad style to have a `<<` operator for `Bar`, or `Bar` may already have a `<<` operator that doesn't do what you want (and you cannot change it). If so, you can instead define a `PrintTo()` function like this: ```c++ // Streams are allowed only for logging. Don't include this for // any other purpose. #include namespace foo { class Bar { ... friend void PrintTo(const Bar& bar, std::ostream* os) { *os << bar.DebugString(); // whatever needed to print bar to os } }; // If you can't declare the function in the class it's important that PrintTo() // is defined in the SAME namespace that defines Bar. C++'s look-up rules rely // on that. void PrintTo(const Bar& bar, std::ostream* os) { *os << bar.DebugString(); // whatever needed to print bar to os } } // namespace foo ``` If you have defined both `<<` and `PrintTo()`, the latter will be used when googletest is concerned. This allows you to customize how the value appears in googletest's output without affecting code that relies on the behavior of its `<<` operator. If you want to print a value `x` using googletest's value printer yourself, just call `::testing::PrintToString(x)`, which returns an `std::string`: ```c++ vector > bar_ints = GetBarIntVector(); EXPECT_TRUE(IsCorrectBarIntVector(bar_ints)) << "bar_ints = " << ::testing::PrintToString(bar_ints); ``` ## Death Tests In many applications, there are assertions that can cause application failure if a condition is not met. These sanity checks, which ensure that the program is in a known good state, are there to fail at the earliest possible time after some program state is corrupted. If the assertion checks the wrong condition, then the program may proceed in an erroneous state, which could lead to memory corruption, security holes, or worse. Hence it is vitally important to test that such assertion statements work as expected. Since these precondition checks cause the processes to die, we call such tests _death tests_. More generally, any test that checks that a program terminates (except by throwing an exception) in an expected fashion is also a death test. Note that if a piece of code throws an exception, we don't consider it "death" for the purpose of death tests, as the caller of the code could catch the exception and avoid the crash. If you want to verify exceptions thrown by your code, see [Exception Assertions](#exception-assertions). If you want to test `EXPECT_*()/ASSERT_*()` failures in your test code, see Catching Failures ### How to Write a Death Test googletest has the following macros to support death tests: Fatal assertion | Nonfatal assertion | Verifies ---------------------------------------------- | ---------------------------------------------- | -------- `ASSERT_DEATH(statement, regex);` | `EXPECT_DEATH(statement, regex);` | `statement` crashes with the given error `ASSERT_DEATH_IF_SUPPORTED(statement, regex);` | `EXPECT_DEATH_IF_SUPPORTED(statement, regex);` | if death tests are supported, verifies that `statement` crashes with the given error; otherwise verifies nothing `ASSERT_EXIT(statement, predicate, regex);` | `EXPECT_EXIT(statement, predicate, regex);` | `statement` exits with the given error, and its exit code matches `predicate` where `statement` is a statement that is expected to cause the process to die, `predicate` is a function or function object that evaluates an integer exit status, and `regex` is a (Perl) regular expression that the stderr output of `statement` is expected to match. Note that `statement` can be *any valid statement* (including *compound statement*) and doesn't have to be an expression. As usual, the `ASSERT` variants abort the current test function, while the `EXPECT` variants do not. > NOTE: We use the word "crash" here to mean that the process terminates with a > *non-zero* exit status code. There are two possibilities: either the process > has called `exit()` or `_exit()` with a non-zero value, or it may be killed by > a signal. > > This means that if `*statement*` terminates the process with a 0 exit code, it > is *not* considered a crash by `EXPECT_DEATH`. Use `EXPECT_EXIT` instead if > this is the case, or if you want to restrict the exit code more precisely. A predicate here must accept an `int` and return a `bool`. The death test succeeds only if the predicate returns `true`. googletest defines a few predicates that handle the most common cases: ```c++ ::testing::ExitedWithCode(exit_code) ``` This expression is `true` if the program exited normally with the given exit code. ```c++ ::testing::KilledBySignal(signal_number) // Not available on Windows. ``` This expression is `true` if the program was killed by the given signal. The `*_DEATH` macros are convenient wrappers for `*_EXIT` that use a predicate that verifies the process' exit code is non-zero. Note that a death test only cares about three things: 1. does `statement` abort or exit the process? 2. (in the case of `ASSERT_EXIT` and `EXPECT_EXIT`) does the exit status satisfy `predicate`? Or (in the case of `ASSERT_DEATH` and `EXPECT_DEATH`) is the exit status non-zero? And 3. does the stderr output match `regex`? In particular, if `statement` generates an `ASSERT_*` or `EXPECT_*` failure, it will **not** cause the death test to fail, as googletest assertions don't abort the process. To write a death test, simply use one of the above macros inside your test function. For example, ```c++ TEST(MyDeathTest, Foo) { // This death test uses a compound statement. ASSERT_DEATH({ int n = 5; Foo(&n); }, "Error on line .* of Foo()"); } TEST(MyDeathTest, NormalExit) { EXPECT_EXIT(NormalExit(), ::testing::ExitedWithCode(0), "Success"); } TEST(MyDeathTest, KillMyself) { EXPECT_EXIT(KillMyself(), ::testing::KilledBySignal(SIGKILL), "Sending myself unblockable signal"); } ``` verifies that: * calling `Foo(5)` causes the process to die with the given error message, * calling `NormalExit()` causes the process to print `"Success"` to stderr and exit with exit code 0, and * calling `KillMyself()` kills the process with signal `SIGKILL`. The test function body may contain other assertions and statements as well, if necessary. ### Death Test Naming IMPORTANT: We strongly recommend you to follow the convention of naming your **test suite** (not test) `*DeathTest` when it contains a death test, as demonstrated in the above example. The [Death Tests And Threads](#death-tests-and-threads) section below explains why. If a test fixture class is shared by normal tests and death tests, you can use `using` or `typedef` to introduce an alias for the fixture class and avoid duplicating its code: ```c++ class FooTest : public ::testing::Test { ... }; using FooDeathTest = FooTest; TEST_F(FooTest, DoesThis) { // normal test } TEST_F(FooDeathTest, DoesThat) { // death test } ``` **Availability**: Linux, Windows, Cygwin, and Mac ### Regular Expression Syntax On POSIX systems (e.g. Linux, Cygwin, and Mac), googletest uses the [POSIX extended regular expression](http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap09.html#tag_09_04) syntax. To learn about this syntax, you may want to read this [Wikipedia entry](http://en.wikipedia.org/wiki/Regular_expression#POSIX_Extended_Regular_Expressions). On Windows, googletest uses its own simple regular expression implementation. It lacks many features. For example, we don't support union (`"x|y"`), grouping (`"(xy)"`), brackets (`"[xy]"`), and repetition count (`"x{5,7}"`), among others. Below is what we do support (`A` denotes a literal character, period (`.`), or a single `\\ ` escape sequence; `x` and `y` denote regular expressions.): Expression | Meaning ---------- | -------------------------------------------------------------- `c` | matches any literal character `c` `\\d` | matches any decimal digit `\\D` | matches any character that's not a decimal digit `\\f` | matches `\f` `\\n` | matches `\n` `\\r` | matches `\r` `\\s` | matches any ASCII whitespace, including `\n` `\\S` | matches any character that's not a whitespace `\\t` | matches `\t` `\\v` | matches `\v` `\\w` | matches any letter, `_`, or decimal digit `\\W` | matches any character that `\\w` doesn't match `\\c` | matches any literal character `c`, which must be a punctuation `.` | matches any single character except `\n` `A?` | matches 0 or 1 occurrences of `A` `A*` | matches 0 or many occurrences of `A` `A+` | matches 1 or many occurrences of `A` `^` | matches the beginning of a string (not that of each line) `$` | matches the end of a string (not that of each line) `xy` | matches `x` followed by `y` To help you determine which capability is available on your system, googletest defines macros to govern which regular expression it is using. The macros are: `GTEST_USES_PCRE=1`, or `GTEST_USES_SIMPLE_RE=1` or `GTEST_USES_POSIX_RE=1`. If you want your death tests to work in all cases, you can either `#if` on these macros or use the more limited syntax only. ### How It Works Under the hood, `ASSERT_EXIT()` spawns a new process and executes the death test statement in that process. The details of how precisely that happens depend on the platform and the variable ::testing::GTEST_FLAG(death_test_style) (which is initialized from the command-line flag `--gtest_death_test_style`). * On POSIX systems, `fork()` (or `clone()` on Linux) is used to spawn the child, after which: * If the variable's value is `"fast"`, the death test statement is immediately executed. * If the variable's value is `"threadsafe"`, the child process re-executes the unit test binary just as it was originally invoked, but with some extra flags to cause just the single death test under consideration to be run. * On Windows, the child is spawned using the `CreateProcess()` API, and re-executes the binary to cause just the single death test under consideration to be run - much like the `threadsafe` mode on POSIX. Other values for the variable are illegal and will cause the death test to fail. Currently, the flag's default value is "fast". However, we reserve the right to change it in the future. Therefore, your tests should not depend on this. In either case, the parent process waits for the child process to complete, and checks that 1. the child's exit status satisfies the predicate, and 2. the child's stderr matches the regular expression. If the death test statement runs to completion without dying, the child process will nonetheless terminate, and the assertion fails. ### Death Tests And Threads The reason for the two death test styles has to do with thread safety. Due to well-known problems with forking in the presence of threads, death tests should be run in a single-threaded context. Sometimes, however, it isn't feasible to arrange that kind of environment. For example, statically-initialized modules may start threads before main is ever reached. Once threads have been created, it may be difficult or impossible to clean them up. googletest has three features intended to raise awareness of threading issues. 1. A warning is emitted if multiple threads are running when a death test is encountered. 2. Test suites with a name ending in "DeathTest" are run before all other tests. 3. It uses `clone()` instead of `fork()` to spawn the child process on Linux (`clone()` is not available on Cygwin and Mac), as `fork()` is more likely to cause the child to hang when the parent process has multiple threads. It's perfectly fine to create threads inside a death test statement; they are executed in a separate process and cannot affect the parent. ### Death Test Styles The "threadsafe" death test style was introduced in order to help mitigate the risks of testing in a possibly multithreaded environment. It trades increased test execution time (potentially dramatically so) for improved thread safety. The automated testing framework does not set the style flag. You can choose a particular style of death tests by setting the flag programmatically: ```c++ testing::FLAGS_gtest_death_test_style="threadsafe" ``` You can do this in `main()` to set the style for all death tests in the binary, or in individual tests. Recall that flags are saved before running each test and restored afterwards, so you need not do that yourself. For example: ```c++ int main(int argc, char** argv) { InitGoogle(argv[0], &argc, &argv, true); ::testing::FLAGS_gtest_death_test_style = "fast"; return RUN_ALL_TESTS(); } TEST(MyDeathTest, TestOne) { ::testing::FLAGS_gtest_death_test_style = "threadsafe"; // This test is run in the "threadsafe" style: ASSERT_DEATH(ThisShouldDie(), ""); } TEST(MyDeathTest, TestTwo) { // This test is run in the "fast" style: ASSERT_DEATH(ThisShouldDie(), ""); } ``` ### Caveats The `statement` argument of `ASSERT_EXIT()` can be any valid C++ statement. If it leaves the current function via a `return` statement or by throwing an exception, the death test is considered to have failed. Some googletest macros may return from the current function (e.g. `ASSERT_TRUE()`), so be sure to avoid them in `statement`. Since `statement` runs in the child process, any in-memory side effect (e.g. modifying a variable, releasing memory, etc) it causes will *not* be observable in the parent process. In particular, if you release memory in a death test, your program will fail the heap check as the parent process will never see the memory reclaimed. To solve this problem, you can 1. try not to free memory in a death test; 2. free the memory again in the parent process; or 3. do not use the heap checker in your program. Due to an implementation detail, you cannot place multiple death test assertions on the same line; otherwise, compilation will fail with an unobvious error message. Despite the improved thread safety afforded by the "threadsafe" style of death test, thread problems such as deadlock are still possible in the presence of handlers registered with `pthread_atfork(3)`. ## Using Assertions in Sub-routines ### Adding Traces to Assertions If a test sub-routine is called from several places, when an assertion inside it fails, it can be hard to tell which invocation of the sub-routine the failure is from. You can alleviate this problem using extra logging or custom failure messages, but that usually clutters up your tests. A better solution is to use the `SCOPED_TRACE` macro or the `ScopedTrace` utility: ```c++ SCOPED_TRACE(message); ScopedTrace trace("file_path", line_number, message); ``` where `message` can be anything streamable to `std::ostream`. `SCOPED_TRACE` macro will cause the current file name, line number, and the given message to be added in every failure message. `ScopedTrace` accepts explicit file name and line number in arguments, which is useful for writing test helpers. The effect will be undone when the control leaves the current lexical scope. For example, ```c++ 10: void Sub1(int n) { 11: EXPECT_EQ(1, Bar(n)); 12: EXPECT_EQ(2, Bar(n + 1)); 13: } 14: 15: TEST(FooTest, Bar) { 16: { 17: SCOPED_TRACE("A"); // This trace point will be included in 18: // every failure in this scope. 19: Sub1(1); 20: } 21: // Now it won't. 22: Sub1(9); 23: } ``` could result in messages like these: ```none path/to/foo_test.cc:11: Failure Value of: Bar(n) Expected: 1 Actual: 2 Trace: path/to/foo_test.cc:17: A path/to/foo_test.cc:12: Failure Value of: Bar(n + 1) Expected: 2 Actual: 3 ``` Without the trace, it would've been difficult to know which invocation of `Sub1()` the two failures come from respectively. (You could add an extra message to each assertion in `Sub1()` to indicate the value of `n`, but that's tedious.) Some tips on using `SCOPED_TRACE`: 1. With a suitable message, it's often enough to use `SCOPED_TRACE` at the beginning of a sub-routine, instead of at each call site. 2. When calling sub-routines inside a loop, make the loop iterator part of the message in `SCOPED_TRACE` such that you can know which iteration the failure is from. 3. Sometimes the line number of the trace point is enough for identifying the particular invocation of a sub-routine. In this case, you don't have to choose a unique message for `SCOPED_TRACE`. You can simply use `""`. 4. You can use `SCOPED_TRACE` in an inner scope when there is one in the outer scope. In this case, all active trace points will be included in the failure messages, in reverse order they are encountered. 5. The trace dump is clickable in Emacs - hit `return` on a line number and you'll be taken to that line in the source file! **Availability**: Linux, Windows, Mac. ### Propagating Fatal Failures A common pitfall when using `ASSERT_*` and `FAIL*` is not understanding that when they fail they only abort the _current function_, not the entire test. For example, the following test will segfault: ```c++ void Subroutine() { // Generates a fatal failure and aborts the current function. ASSERT_EQ(1, 2); // The following won't be executed. ... } TEST(FooTest, Bar) { Subroutine(); // The intended behavior is for the fatal failure // in Subroutine() to abort the entire test. // The actual behavior: the function goes on after Subroutine() returns. int* p = NULL; *p = 3; // Segfault! } ``` To alleviate this, googletest provides three different solutions. You could use either exceptions, the `(ASSERT|EXPECT)_NO_FATAL_FAILURE` assertions or the `HasFatalFailure()` function. They are described in the following two subsections. #### Asserting on Subroutines with an exception The following code can turn ASSERT-failure into an exception: ```c++ class ThrowListener : public testing::EmptyTestEventListener { void OnTestPartResult(const testing::TestPartResult& result) override { if (result.type() == testing::TestPartResult::kFatalFailure) { throw testing::AssertionException(result); } } }; int main(int argc, char** argv) { ... testing::UnitTest::GetInstance()->listeners().Append(new ThrowListener); return RUN_ALL_TESTS(); } ``` This listener should be added after other listeners if you have any, otherwise they won't see failed `OnTestPartResult`. #### Asserting on Subroutines As shown above, if your test calls a subroutine that has an `ASSERT_*` failure in it, the test will continue after the subroutine returns. This may not be what you want. Often people want fatal failures to propagate like exceptions. For that googletest offers the following macros: Fatal assertion | Nonfatal assertion | Verifies ------------------------------------- | ------------------------------------- | -------- `ASSERT_NO_FATAL_FAILURE(statement);` | `EXPECT_NO_FATAL_FAILURE(statement);` | `statement` doesn't generate any new fatal failures in the current thread. Only failures in the thread that executes the assertion are checked to determine the result of this type of assertions. If `statement` creates new threads, failures in these threads are ignored. Examples: ```c++ ASSERT_NO_FATAL_FAILURE(Foo()); int i; EXPECT_NO_FATAL_FAILURE({ i = Bar(); }); ``` **Availability**: Linux, Windows, Mac. Assertions from multiple threads are currently not supported on Windows. #### Checking for Failures in the Current Test `HasFatalFailure()` in the `::testing::Test` class returns `true` if an assertion in the current test has suffered a fatal failure. This allows functions to catch fatal failures in a sub-routine and return early. ```c++ class Test { public: ... static bool HasFatalFailure(); }; ``` The typical usage, which basically simulates the behavior of a thrown exception, is: ```c++ TEST(FooTest, Bar) { Subroutine(); // Aborts if Subroutine() had a fatal failure. if (HasFatalFailure()) return; // The following won't be executed. ... } ``` If `HasFatalFailure()` is used outside of `TEST()` , `TEST_F()` , or a test fixture, you must add the `::testing::Test::` prefix, as in: ```c++ if (::testing::Test::HasFatalFailure()) return; ``` Similarly, `HasNonfatalFailure()` returns `true` if the current test has at least one non-fatal failure, and `HasFailure()` returns `true` if the current test has at least one failure of either kind. **Availability**: Linux, Windows, Mac. ## Logging Additional Information In your test code, you can call `RecordProperty("key", value)` to log additional information, where `value` can be either a string or an `int`. The *last* value recorded for a key will be emitted to the [XML output](#generating-an-xml-report) if you specify one. For example, the test ```c++ TEST_F(WidgetUsageTest, MinAndMaxWidgets) { RecordProperty("MaximumWidgets", ComputeMaxUsage()); RecordProperty("MinimumWidgets", ComputeMinUsage()); } ``` will output XML like this: ```xml ... ... ``` > NOTE: > > * `RecordProperty()` is a static member of the `Test` class. Therefore it > needs to be prefixed with `::testing::Test::` if used outside of the > `TEST` body and the test fixture class. > * `*key*` must be a valid XML attribute name, and cannot conflict with the > ones already used by googletest (`name`, `status`, `time`, `classname`, > `type_param`, and `value_param`). > * Calling `RecordProperty()` outside of the lifespan of a test is allowed. > If it's called outside of a test but between a test suite's > `SetUpTestSuite()` and `TearDownTestSuite()` methods, it will be attributed > to the XML element for the test suite. If it's called outside of all test > suites (e.g. in a test environment), it will be attributed to the top-level > XML element. **Availability**: Linux, Windows, Mac. ## Sharing Resources Between Tests in the Same Test Suite googletest creates a new test fixture object for each test in order to make tests independent and easier to debug. However, sometimes tests use resources that are expensive to set up, making the one-copy-per-test model prohibitively expensive. If the tests don't change the resource, there's no harm in their sharing a single resource copy. So, in addition to per-test set-up/tear-down, googletest also supports per-test-suite set-up/tear-down. To use it: 1. In your test fixture class (say `FooTest` ), declare as `static` some member variables to hold the shared resources. 1. Outside your test fixture class (typically just below it), define those member variables, optionally giving them initial values. 1. In the same test fixture class, define a `static void SetUpTestSuite()` function (remember not to spell it as **`SetupTestSuite`** with a small `u`!) to set up the shared resources and a `static void TearDownTestSuite()` function to tear them down. That's it! googletest automatically calls `SetUpTestSuite()` before running the *first test* in the `FooTest` test suite (i.e. before creating the first `FooTest` object), and calls `TearDownTestSuite()` after running the *last test* in it (i.e. after deleting the last `FooTest` object). In between, the tests can use the shared resources. Remember that the test order is undefined, so your code can't depend on a test preceding or following another. Also, the tests must either not modify the state of any shared resource, or, if they do modify the state, they must restore the state to its original value before passing control to the next test. Here's an example of per-test-suite set-up and tear-down: ```c++ class FooTest : public ::testing::Test { protected: // Per-test-suite set-up. // Called before the first test in this test suite. // Can be omitted if not needed. static void SetUpTestSuite() { shared_resource_ = new ...; } // Per-test-suite tear-down. // Called after the last test in this test suite. // Can be omitted if not needed. static void TearDownTestSuite() { delete shared_resource_; shared_resource_ = NULL; } // You can define per-test set-up logic as usual. virtual void SetUp() { ... } // You can define per-test tear-down logic as usual. virtual void TearDown() { ... } // Some expensive resource shared by all tests. static T* shared_resource_; }; T* FooTest::shared_resource_ = NULL; TEST_F(FooTest, Test1) { ... you can refer to shared_resource_ here ... } TEST_F(FooTest, Test2) { ... you can refer to shared_resource_ here ... } ``` NOTE: Though the above code declares `SetUpTestSuite()` protected, it may sometimes be necessary to declare it public, such as when using it with `TEST_P`. **Availability**: Linux, Windows, Mac. ## Global Set-Up and Tear-Down Just as you can do set-up and tear-down at the test level and the test suite level, you can also do it at the test program level. Here's how. First, you subclass the `::testing::Environment` class to define a test environment, which knows how to set-up and tear-down: ```c++ class Environment { public: virtual ~Environment() {} // Override this to define how to set up the environment. virtual void SetUp() {} // Override this to define how to tear down the environment. virtual void TearDown() {} }; ``` Then, you register an instance of your environment class with googletest by calling the `::testing::AddGlobalTestEnvironment()` function: ```c++ Environment* AddGlobalTestEnvironment(Environment* env); ``` Now, when `RUN_ALL_TESTS()` is called, it first calls the `SetUp()` method of each environment object, then runs the tests if none of the environments reported fatal failures and `GTEST_SKIP()` was not called. `RUN_ALL_TESTS()` always calls `TearDown()` with each environment object, regardless of whether or not the tests were run. It's OK to register multiple environment objects. In this case, their `SetUp()` will be called in the order they are registered, and their `TearDown()` will be called in the reverse order. Note that googletest takes ownership of the registered environment objects. Therefore **do not delete them** by yourself. You should call `AddGlobalTestEnvironment()` before `RUN_ALL_TESTS()` is called, probably in `main()`. If you use `gtest_main`, you need to call this before `main()` starts for it to take effect. One way to do this is to define a global variable like this: ```c++ ::testing::Environment* const foo_env = ::testing::AddGlobalTestEnvironment(new FooEnvironment); ``` However, we strongly recommend you to write your own `main()` and call `AddGlobalTestEnvironment()` there, as relying on initialization of global variables makes the code harder to read and may cause problems when you register multiple environments from different translation units and the environments have dependencies among them (remember that the compiler doesn't guarantee the order in which global variables from different translation units are initialized). ## Value-Parameterized Tests *Value-parameterized tests* allow you to test your code with different parameters without writing multiple copies of the same test. This is useful in a number of situations, for example: * You have a piece of code whose behavior is affected by one or more command-line flags. You want to make sure your code performs correctly for various values of those flags. * You want to test different implementations of an OO interface. * You want to test your code over various inputs (a.k.a. data-driven testing). This feature is easy to abuse, so please exercise your good sense when doing it! ### How to Write Value-Parameterized Tests To write value-parameterized tests, first you should define a fixture class. It must be derived from both `::testing::Test` and `::testing::WithParamInterface` (the latter is a pure interface), where `T` is the type of your parameter values. For convenience, you can just derive the fixture class from `::testing::TestWithParam`, which itself is derived from both `::testing::Test` and `::testing::WithParamInterface`. `T` can be any copyable type. If it's a raw pointer, you are responsible for managing the lifespan of the pointed values. NOTE: If your test fixture defines `SetUpTestSuite()` or `TearDownTestSuite()` they must be declared **public** rather than **protected** in order to use `TEST_P`. ```c++ class FooTest : public ::testing::TestWithParam { // You can implement all the usual fixture class members here. // To access the test parameter, call GetParam() from class // TestWithParam. }; // Or, when you want to add parameters to a pre-existing fixture class: class BaseTest : public ::testing::Test { ... }; class BarTest : public BaseTest, public ::testing::WithParamInterface { ... }; ``` Then, use the `TEST_P` macro to define as many test patterns using this fixture as you want. The `_P` suffix is for "parameterized" or "pattern", whichever you prefer to think. ```c++ TEST_P(FooTest, DoesBlah) { // Inside a test, access the test parameter with the GetParam() method // of the TestWithParam class: EXPECT_TRUE(foo.Blah(GetParam())); ... } TEST_P(FooTest, HasBlahBlah) { ... } ``` Finally, you can use `INSTANTIATE_TEST_SUITE_P` to instantiate the test suite with any set of parameters you want. googletest defines a number of functions for generating test parameters. They return what we call (surprise!) *parameter generators*. Here is a summary of them, which are all in the `testing` namespace: | Parameter Generator | Behavior | | ---------------------------- | ------------------------------------------- | | `Range(begin, end [, step])` | Yields values `{begin, begin+step, begin+step+step, ...}`. The values do not include `end`. `step` defaults to 1. | | `Values(v1, v2, ..., vN)` | Yields values `{v1, v2, ..., vN}`. | | `ValuesIn(container)` and `ValuesIn(begin,end)` | Yields values from a C-style array, an STL-style container, or an iterator range `[begin, end)`. | | `Bool()` | Yields sequence `{false, true}`. | | `Combine(g1, g2, ..., gN)` | Yields all combinations (Cartesian product) as std\:\:tuples of the values generated by the `N` generators. | For more details, see the comments at the definitions of these functions. NOTE: The `INSTANTIATE_TEST_SUITE_P` keyword is recommended (addressing https://github.com/google/googletest/issues/1085) For 1.8.1 and previous releases the keyword is `INSTANTIATE_TEST_CASE_P`. which has been deprecated in favor of INSTANTIATE_TEST_SUITE_P. The following statement will instantiate tests from the `FooTest` test suite each with parameter values `"meeny"`, `"miny"`, and `"moe"`. ```c++ INSTANTIATE_TEST_SUITE_P(InstantiationName, FooTest, ::testing::Values("meeny", "miny", "moe")); ``` NOTE: The code above must be placed at global or namespace scope, not at function scope. NOTE: Don't forget this step! If you do your test will silently pass, but none of its suites will ever run! To distinguish different instances of the pattern (yes, you can instantiate it more than once), the first argument to `INSTANTIATE_TEST_SUITE_P` is a prefix that will be added to the actual test suite name. Remember to pick unique prefixes for different instantiations. The tests from the instantiation above will have these names: * `InstantiationName/FooTest.DoesBlah/0` for `"meeny"` * `InstantiationName/FooTest.DoesBlah/1` for `"miny"` * `InstantiationName/FooTest.DoesBlah/2` for `"moe"` * `InstantiationName/FooTest.HasBlahBlah/0` for `"meeny"` * `InstantiationName/FooTest.HasBlahBlah/1` for `"miny"` * `InstantiationName/FooTest.HasBlahBlah/2` for `"moe"` You can use these names in [`--gtest_filter`](#running-a-subset-of-the-tests). This statement will instantiate all tests from `FooTest` again, each with parameter values `"cat"` and `"dog"`: ```c++ const char* pets[] = {"cat", "dog"}; INSTANTIATE_TEST_SUITE_P(AnotherInstantiationName, FooTest, ::testing::ValuesIn(pets)); ``` The tests from the instantiation above will have these names: * `AnotherInstantiationName/FooTest.DoesBlah/0` for `"cat"` * `AnotherInstantiationName/FooTest.DoesBlah/1` for `"dog"` * `AnotherInstantiationName/FooTest.HasBlahBlah/0` for `"cat"` * `AnotherInstantiationName/FooTest.HasBlahBlah/1` for `"dog"` Please note that `INSTANTIATE_TEST_SUITE_P` will instantiate *all* tests in the given test suite, whether their definitions come before or *after* the `INSTANTIATE_TEST_SUITE_P` statement. You can see sample7_unittest.cc and sample8_unittest.cc for more examples. **Availability**: Linux, Windows, Mac ### Creating Value-Parameterized Abstract Tests In the above, we define and instantiate `FooTest` in the *same* source file. Sometimes you may want to define value-parameterized tests in a library and let other people instantiate them later. This pattern is known as *abstract tests*. As an example of its application, when you are designing an interface you can write a standard suite of abstract tests (perhaps using a factory function as the test parameter) that all implementations of the interface are expected to pass. When someone implements the interface, they can instantiate your suite to get all the interface-conformance tests for free. To define abstract tests, you should organize your code like this: 1. Put the definition of the parameterized test fixture class (e.g. `FooTest`) in a header file, say `foo_param_test.h`. Think of this as *declaring* your abstract tests. 1. Put the `TEST_P` definitions in `foo_param_test.cc`, which includes `foo_param_test.h`. Think of this as *implementing* your abstract tests. Once they are defined, you can instantiate them by including `foo_param_test.h`, invoking `INSTANTIATE_TEST_SUITE_P()`, and depending on the library target that contains `foo_param_test.cc`. You can instantiate the same abstract test suite multiple times, possibly in different source files. ### Specifying Names for Value-Parameterized Test Parameters The optional last argument to `INSTANTIATE_TEST_SUITE_P()` allows the user to specify a function or functor that generates custom test name suffixes based on the test parameters. The function should accept one argument of type `testing::TestParamInfo`, and return `std::string`. `testing::PrintToStringParamName` is a builtin test suffix generator that returns the value of `testing::PrintToString(GetParam())`. It does not work for `std::string` or C strings. NOTE: test names must be non-empty, unique, and may only contain ASCII alphanumeric characters. In particular, they [should not contain underscores](https://github.com/google/googletest/blob/master/googletest/docs/faq.md#why-should-test-suite-names-and-test-names-not-contain-underscore). ```c++ class MyTestsuite : public testing::TestWithParam {}; TEST_P(MyTestsuite, MyTest) { std::cout << "Example Test Param: " << GetParam() << std::endl; } INSTANTIATE_TEST_SUITE_P(MyGroup, MyTestsuite, testing::Range(0, 10), testing::PrintToStringParamName()); ``` ## Typed Tests Suppose you have multiple implementations of the same interface and want to make sure that all of them satisfy some common requirements. Or, you may have defined several types that are supposed to conform to the same "concept" and you want to verify it. In both cases, you want the same test logic repeated for different types. While you can write one `TEST` or `TEST_F` for each type you want to test (and you may even factor the test logic into a function template that you invoke from the `TEST`), it's tedious and doesn't scale: if you want `m` tests over `n` types, you'll end up writing `m*n` `TEST`s. *Typed tests* allow you to repeat the same test logic over a list of types. You only need to write the test logic once, although you must know the type list when writing typed tests. Here's how you do it: First, define a fixture class template. It should be parameterized by a type. Remember to derive it from `::testing::Test`: ```c++ template class FooTest : public ::testing::Test { public: ... typedef std::list List; static T shared_; T value_; }; ``` Next, associate a list of types with the test suite, which will be repeated for each type in the list: ```c++ using MyTypes = ::testing::Types; TYPED_TEST_SUITE(FooTest, MyTypes); ``` The type alias (`using` or `typedef`) is necessary for the `TYPED_TEST_SUITE` macro to parse correctly. Otherwise the compiler will think that each comma in the type list introduces a new macro argument. Then, use `TYPED_TEST()` instead of `TEST_F()` to define a typed test for this test suite. You can repeat this as many times as you want: ```c++ TYPED_TEST(FooTest, DoesBlah) { // Inside a test, refer to the special name TypeParam to get the type // parameter. Since we are inside a derived class template, C++ requires // us to visit the members of FooTest via 'this'. TypeParam n = this->value_; // To visit static members of the fixture, add the 'TestFixture::' // prefix. n += TestFixture::shared_; // To refer to typedefs in the fixture, add the 'typename TestFixture::' // prefix. The 'typename' is required to satisfy the compiler. typename TestFixture::List values; values.push_back(n); ... } TYPED_TEST(FooTest, HasPropertyA) { ... } ``` You can see sample6_unittest.cc **Availability**: Linux, Windows, Mac ## Type-Parameterized Tests *Type-parameterized tests* are like typed tests, except that they don't require you to know the list of types ahead of time. Instead, you can define the test logic first and instantiate it with different type lists later. You can even instantiate it more than once in the same program. If you are designing an interface or concept, you can define a suite of type-parameterized tests to verify properties that any valid implementation of the interface/concept should have. Then, the author of each implementation can just instantiate the test suite with their type to verify that it conforms to the requirements, without having to write similar tests repeatedly. Here's an example: First, define a fixture class template, as we did with typed tests: ```c++ template class FooTest : public ::testing::Test { ... }; ``` Next, declare that you will define a type-parameterized test suite: ```c++ TYPED_TEST_SUITE_P(FooTest); ``` Then, use `TYPED_TEST_P()` to define a type-parameterized test. You can repeat this as many times as you want: ```c++ TYPED_TEST_P(FooTest, DoesBlah) { // Inside a test, refer to TypeParam to get the type parameter. TypeParam n = 0; ... } TYPED_TEST_P(FooTest, HasPropertyA) { ... } ``` Now the tricky part: you need to register all test patterns using the `REGISTER_TYPED_TEST_SUITE_P` macro before you can instantiate them. The first argument of the macro is the test suite name; the rest are the names of the tests in this test suite: ```c++ REGISTER_TYPED_TEST_SUITE_P(FooTest, DoesBlah, HasPropertyA); ``` Finally, you are free to instantiate the pattern with the types you want. If you put the above code in a header file, you can `#include` it in multiple C++ source files and instantiate it multiple times. ```c++ typedef ::testing::Types MyTypes; INSTANTIATE_TYPED_TEST_SUITE_P(My, FooTest, MyTypes); ``` To distinguish different instances of the pattern, the first argument to the `INSTANTIATE_TYPED_TEST_SUITE_P` macro is a prefix that will be added to the actual test suite name. Remember to pick unique prefixes for different instances. In the special case where the type list contains only one type, you can write that type directly without `::testing::Types<...>`, like this: ```c++ INSTANTIATE_TYPED_TEST_SUITE_P(My, FooTest, int); ``` You can see `sample6_unittest.cc` for a complete example. **Availability**: Linux, Windows, Mac ## Testing Private Code If you change your software's internal implementation, your tests should not break as long as the change is not observable by users. Therefore, **per the black-box testing principle, most of the time you should test your code through its public interfaces.** **If you still find yourself needing to test internal implementation code, consider if there's a better design.** The desire to test internal implementation is often a sign that the class is doing too much. Consider extracting an implementation class, and testing it. Then use that implementation class in the original class. If you absolutely have to test non-public interface code though, you can. There are two cases to consider: * Static functions ( *not* the same as static member functions!) or unnamed namespaces, and * Private or protected class members To test them, we use the following special techniques: * Both static functions and definitions/declarations in an unnamed namespace are only visible within the same translation unit. To test them, you can `#include` the entire `.cc` file being tested in your `*_test.cc` file. (including `.cc` files is not a good way to reuse code - you should not do this in production code!) However, a better approach is to move the private code into the `foo::internal` namespace, where `foo` is the namespace your project normally uses, and put the private declarations in a `*-internal.h` file. Your production `.cc` files and your tests are allowed to include this internal header, but your clients are not. This way, you can fully test your internal implementation without leaking it to your clients. * Private class members are only accessible from within the class or by friends. To access a class' private members, you can declare your test fixture as a friend to the class and define accessors in your fixture. Tests using the fixture can then access the private members of your production class via the accessors in the fixture. Note that even though your fixture is a friend to your production class, your tests are not automatically friends to it, as they are technically defined in sub-classes of the fixture. Another way to test private members is to refactor them into an implementation class, which is then declared in a `*-internal.h` file. Your clients aren't allowed to include this header but your tests can. Such is called the [Pimpl](https://www.gamedev.net/articles/programming/general-and-gameplay-programming/the-c-pimpl-r1794/) (Private Implementation) idiom. Or, you can declare an individual test as a friend of your class by adding this line in the class body: ```c++ FRIEND_TEST(TestsuiteName, TestName); ``` For example, ```c++ // foo.h #include "gtest/gtest_prod.h" class Foo { ... private: FRIEND_TEST(FooTest, BarReturnsZeroOnNull); int Bar(void* x); }; // foo_test.cc ... TEST(FooTest, BarReturnsZeroOnNull) { Foo foo; EXPECT_EQ(0, foo.Bar(NULL)); // Uses Foo's private member Bar(). } ``` Pay special attention when your class is defined in a namespace, as you should define your test fixtures and tests in the same namespace if you want them to be friends of your class. For example, if the code to be tested looks like: ```c++ namespace my_namespace { class Foo { friend class FooTest; FRIEND_TEST(FooTest, Bar); FRIEND_TEST(FooTest, Baz); ... definition of the class Foo ... }; } // namespace my_namespace ``` Your test code should be something like: ```c++ namespace my_namespace { class FooTest : public ::testing::Test { protected: ... }; TEST_F(FooTest, Bar) { ... } TEST_F(FooTest, Baz) { ... } } // namespace my_namespace ``` ## "Catching" Failures If you are building a testing utility on top of googletest, you'll want to test your utility. What framework would you use to test it? googletest, of course. The challenge is to verify that your testing utility reports failures correctly. In frameworks that report a failure by throwing an exception, you could catch the exception and assert on it. But googletest doesn't use exceptions, so how do we test that a piece of code generates an expected failure? gunit-spi.h contains some constructs to do this. After #including this header, you can use ```c++ EXPECT_FATAL_FAILURE(statement, substring); ``` to assert that `statement` generates a fatal (e.g. `ASSERT_*`) failure in the current thread whose message contains the given `substring`, or use ```c++ EXPECT_NONFATAL_FAILURE(statement, substring); ``` if you are expecting a non-fatal (e.g. `EXPECT_*`) failure. Only failures in the current thread are checked to determine the result of this type of expectations. If `statement` creates new threads, failures in these threads are also ignored. If you want to catch failures in other threads as well, use one of the following macros instead: ```c++ EXPECT_FATAL_FAILURE_ON_ALL_THREADS(statement, substring); EXPECT_NONFATAL_FAILURE_ON_ALL_THREADS(statement, substring); ``` NOTE: Assertions from multiple threads are currently not supported on Windows. For technical reasons, there are some caveats: 1. You cannot stream a failure message to either macro. 1. `statement` in `EXPECT_FATAL_FAILURE{_ON_ALL_THREADS}()` cannot reference local non-static variables or non-static members of `this` object. 1. `statement` in `EXPECT_FATAL_FAILURE{_ON_ALL_THREADS}()()` cannot return a value. ## Registering tests programmatically The `TEST` macros handle the vast majority of all use cases, but there are few were runtime registration logic is required. For those cases, the framework provides the `::testing::RegisterTest` that allows callers to register arbitrary tests dynamically. This is an advanced API only to be used when the `TEST` macros are insufficient. The macros should be preferred when possible, as they avoid most of the complexity of calling this function. It provides the following signature: ```c++ template TestInfo* RegisterTest(const char* test_case_name, const char* test_name, const char* type_param, const char* value_param, const char* file, int line, Factory factory); ``` The `factory` argument is a factory callable (move-constructible) object or function pointer that creates a new instance of the Test object. It handles ownership to the caller. The signature of the callable is `Fixture*()`, where `Fixture` is the test fixture class for the test. All tests registered with the same `test_case_name` must return the same fixture type. This is checked at runtime. The framework will infer the fixture class from the factory and will call the `SetUpTestCase` and `TearDownTestCase` for it. Must be called before `RUN_ALL_TESTS()` is invoked, otherwise behavior is undefined. Use case example: ```c++ class MyFixture : public ::testing::Test { public: // All of these optional, just like in regular macro usage. static void SetUpTestCase() { ... } static void TearDownTestCase() { ... } void SetUp() override { ... } void TearDown() override { ... } }; class MyTest : public MyFixture { public: explicit MyTest(int data) : data_(data) {} void TestBody() override { ... } private: int data_; }; void RegisterMyTests(const std::vector& values) { for (int v : values) { ::testing::RegisterTest( "MyFixture", ("Test" + std::to_string(v)).c_str(), nullptr, std::to_string(v).c_str(), __FILE__, __LINE__, // Important to use the fixture type as the return type here. [=]() -> MyFixture* { return new MyTest(v); }); } } ... int main(int argc, char** argv) { std::vector values_to_test = LoadValuesFromConfig(); RegisterMyTests(values_to_test); ... return RUN_ALL_TESTS(); } ``` ## Getting the Current Test's Name Sometimes a function may need to know the name of the currently running test. For example, you may be using the `SetUp()` method of your test fixture to set the golden file name based on which test is running. The `::testing::TestInfo` class has this information: ```c++ namespace testing { class TestInfo { public: // Returns the test suite name and the test name, respectively. // // Do NOT delete or free the return value - it's managed by the // TestInfo class. const char* test_suite_name() const; const char* name() const; }; } ``` To obtain a `TestInfo` object for the currently running test, call `current_test_info()` on the `UnitTest` singleton object: ```c++ // Gets information about the currently running test. // Do NOT delete the returned object - it's managed by the UnitTest class. const ::testing::TestInfo* const test_info = ::testing::UnitTest::GetInstance()->current_test_info(); printf("We are in test %s of test suite %s.\n", test_info->name(), test_info->test_suite_name()); ``` `current_test_info()` returns a null pointer if no test is running. In particular, you cannot find the test suite name in `TestsuiteSetUp()`, `TestsuiteTearDown()` (where you know the test suite name implicitly), or functions called from them. **Availability**: Linux, Windows, Mac. ## Extending googletest by Handling Test Events googletest provides an **event listener API** to let you receive notifications about the progress of a test program and test failures. The events you can listen to include the start and end of the test program, a test suite, or a test method, among others. You may use this API to augment or replace the standard console output, replace the XML output, or provide a completely different form of output, such as a GUI or a database. You can also use test events as checkpoints to implement a resource leak checker, for example. **Availability**: Linux, Windows, Mac. ### Defining Event Listeners To define a event listener, you subclass either testing::TestEventListener or testing::EmptyTestEventListener The former is an (abstract) interface, where *each pure virtual method can be overridden to handle a test event* (For example, when a test starts, the `OnTestStart()` method will be called.). The latter provides an empty implementation of all methods in the interface, such that a subclass only needs to override the methods it cares about. When an event is fired, its context is passed to the handler function as an argument. The following argument types are used: * UnitTest reflects the state of the entire test program, * Testsuite has information about a test suite, which can contain one or more tests, * TestInfo contains the state of a test, and * TestPartResult represents the result of a test assertion. An event handler function can examine the argument it receives to find out interesting information about the event and the test program's state. Here's an example: ```c++ class MinimalistPrinter : public ::testing::EmptyTestEventListener { // Called before a test starts. virtual void OnTestStart(const ::testing::TestInfo& test_info) { printf("*** Test %s.%s starting.\n", test_info.test_suite_name(), test_info.name()); } // Called after a failed assertion or a SUCCESS(). virtual void OnTestPartResult(const ::testing::TestPartResult& test_part_result) { printf("%s in %s:%d\n%s\n", test_part_result.failed() ? "*** Failure" : "Success", test_part_result.file_name(), test_part_result.line_number(), test_part_result.summary()); } // Called after a test ends. virtual void OnTestEnd(const ::testing::TestInfo& test_info) { printf("*** Test %s.%s ending.\n", test_info.test_suite_name(), test_info.name()); } }; ``` ### Using Event Listeners To use the event listener you have defined, add an instance of it to the googletest event listener list (represented by class TestEventListeners - note the "s" at the end of the name) in your `main()` function, before calling `RUN_ALL_TESTS()`: ```c++ int main(int argc, char** argv) { ::testing::InitGoogleTest(&argc, argv); // Gets hold of the event listener list. ::testing::TestEventListeners& listeners = ::testing::UnitTest::GetInstance()->listeners(); // Adds a listener to the end. googletest takes the ownership. listeners.Append(new MinimalistPrinter); return RUN_ALL_TESTS(); } ``` There's only one problem: the default test result printer is still in effect, so its output will mingle with the output from your minimalist printer. To suppress the default printer, just release it from the event listener list and delete it. You can do so by adding one line: ```c++ ... delete listeners.Release(listeners.default_result_printer()); listeners.Append(new MinimalistPrinter); return RUN_ALL_TESTS(); ``` Now, sit back and enjoy a completely different output from your tests. For more details, you can read this sample9_unittest.cc You may append more than one listener to the list. When an `On*Start()` or `OnTestPartResult()` event is fired, the listeners will receive it in the order they appear in the list (since new listeners are added to the end of the list, the default text printer and the default XML generator will receive the event first). An `On*End()` event will be received by the listeners in the *reverse* order. This allows output by listeners added later to be framed by output from listeners added earlier. ### Generating Failures in Listeners You may use failure-raising macros (`EXPECT_*()`, `ASSERT_*()`, `FAIL()`, etc) when processing an event. There are some restrictions: 1. You cannot generate any failure in `OnTestPartResult()` (otherwise it will cause `OnTestPartResult()` to be called recursively). 1. A listener that handles `OnTestPartResult()` is not allowed to generate any failure. When you add listeners to the listener list, you should put listeners that handle `OnTestPartResult()` *before* listeners that can generate failures. This ensures that failures generated by the latter are attributed to the right test by the former. We have a sample of failure-raising listener sample10_unittest.cc ## Running Test Programs: Advanced Options googletest test programs are ordinary executables. Once built, you can run them directly and affect their behavior via the following environment variables and/or command line flags. For the flags to work, your programs must call `::testing::InitGoogleTest()` before calling `RUN_ALL_TESTS()`. To see a list of supported flags and their usage, please run your test program with the `--help` flag. You can also use `-h`, `-?`, or `/?` for short. If an option is specified both by an environment variable and by a flag, the latter takes precedence. ### Selecting Tests #### Listing Test Names Sometimes it is necessary to list the available tests in a program before running them so that a filter may be applied if needed. Including the flag `--gtest_list_tests` overrides all other flags and lists tests in the following format: ```none Testsuite1. TestName1 TestName2 Testsuite2. TestName ``` None of the tests listed are actually run if the flag is provided. There is no corresponding environment variable for this flag. **Availability**: Linux, Windows, Mac. #### Running a Subset of the Tests By default, a googletest program runs all tests the user has defined. Sometimes, you want to run only a subset of the tests (e.g. for debugging or quickly verifying a change). If you set the `GTEST_FILTER` environment variable or the `--gtest_filter` flag to a filter string, googletest will only run the tests whose full names (in the form of `TestsuiteName.TestName`) match the filter. The format of a filter is a '`:`'-separated list of wildcard patterns (called the *positive patterns*) optionally followed by a '`-`' and another '`:`'-separated pattern list (called the *negative patterns*). A test matches the filter if and only if it matches any of the positive patterns but does not match any of the negative patterns. A pattern may contain `'*'` (matches any string) or `'?'` (matches any single character). For convenience, the filter `'*-NegativePatterns'` can be also written as `'-NegativePatterns'`. For example: * `./foo_test` Has no flag, and thus runs all its tests. * `./foo_test --gtest_filter=*` Also runs everything, due to the single match-everything `*` value. * `./foo_test --gtest_filter=FooTest.*` Runs everything in test suite `FooTest` . * `./foo_test --gtest_filter=*Null*:*Constructor*` Runs any test whose full name contains either `"Null"` or `"Constructor"` . * `./foo_test --gtest_filter=-*DeathTest.*` Runs all non-death tests. * `./foo_test --gtest_filter=FooTest.*-FooTest.Bar` Runs everything in test suite `FooTest` except `FooTest.Bar`. * `./foo_test --gtest_filter=FooTest.*:BarTest.*-FooTest.Bar:BarTest.Foo` Runs everything in test suite `FooTest` except `FooTest.Bar` and everything in test suite `BarTest` except `BarTest.Foo`. #### Temporarily Disabling Tests If you have a broken test that you cannot fix right away, you can add the `DISABLED_` prefix to its name. This will exclude it from execution. This is better than commenting out the code or using `#if 0`, as disabled tests are still compiled (and thus won't rot). If you need to disable all tests in a test suite, you can either add `DISABLED_` to the front of the name of each test, or alternatively add it to the front of the test suite name. For example, the following tests won't be run by googletest, even though they will still be compiled: ```c++ // Tests that Foo does Abc. TEST(FooTest, DISABLED_DoesAbc) { ... } class DISABLED_BarTest : public ::testing::Test { ... }; // Tests that Bar does Xyz. TEST_F(DISABLED_BarTest, DoesXyz) { ... } ``` NOTE: This feature should only be used for temporary pain-relief. You still have to fix the disabled tests at a later date. As a reminder, googletest will print a banner warning you if a test program contains any disabled tests. TIP: You can easily count the number of disabled tests you have using `gsearch` and/or `grep`. This number can be used as a metric for improving your test quality. **Availability**: Linux, Windows, Mac. #### Temporarily Enabling Disabled Tests To include disabled tests in test execution, just invoke the test program with the `--gtest_also_run_disabled_tests` flag or set the `GTEST_ALSO_RUN_DISABLED_TESTS` environment variable to a value other than `0`. You can combine this with the `--gtest_filter` flag to further select which disabled tests to run. **Availability**: Linux, Windows, Mac. ### Repeating the Tests Once in a while you'll run into a test whose result is hit-or-miss. Perhaps it will fail only 1% of the time, making it rather hard to reproduce the bug under a debugger. This can be a major source of frustration. The `--gtest_repeat` flag allows you to repeat all (or selected) test methods in a program many times. Hopefully, a flaky test will eventually fail and give you a chance to debug. Here's how to use it: ```none $ foo_test --gtest_repeat=1000 Repeat foo_test 1000 times and don't stop at failures. $ foo_test --gtest_repeat=-1 A negative count means repeating forever. $ foo_test --gtest_repeat=1000 --gtest_break_on_failure Repeat foo_test 1000 times, stopping at the first failure. This is especially useful when running under a debugger: when the test fails, it will drop into the debugger and you can then inspect variables and stacks. $ foo_test --gtest_repeat=1000 --gtest_filter=FooBar.* Repeat the tests whose name matches the filter 1000 times. ``` If your test program contains [global set-up/tear-down](#global-set-up-and-tear-down) code, it will be repeated in each iteration as well, as the flakiness may be in it. You can also specify the repeat count by setting the `GTEST_REPEAT` environment variable. **Availability**: Linux, Windows, Mac. ### Shuffling the Tests You can specify the `--gtest_shuffle` flag (or set the `GTEST_SHUFFLE` environment variable to `1`) to run the tests in a program in a random order. This helps to reveal bad dependencies between tests. By default, googletest uses a random seed calculated from the current time. Therefore you'll get a different order every time. The console output includes the random seed value, such that you can reproduce an order-related test failure later. To specify the random seed explicitly, use the `--gtest_random_seed=SEED` flag (or set the `GTEST_RANDOM_SEED` environment variable), where `SEED` is an integer in the range [0, 99999]. The seed value 0 is special: it tells googletest to do the default behavior of calculating the seed from the current time. If you combine this with `--gtest_repeat=N`, googletest will pick a different random seed and re-shuffle the tests in each iteration. **Availability**: Linux, Windows, Mac. ### Controlling Test Output #### Colored Terminal Output googletest can use colors in its terminal output to make it easier to spot the important information: ...
[----------] 1 test from FooTest
[ RUN ] FooTest.DoesAbc
[ OK ] FooTest.DoesAbc
[----------] 2 tests from BarTest
[ RUN ] BarTest.HasXyzProperty
[ OK ] BarTest.HasXyzProperty
[ RUN ] BarTest.ReturnsTrueOnSuccess
... some error messages ...
[ FAILED ] BarTest.ReturnsTrueOnSuccess
...
[==========] 30 tests from 14 test suites ran.
[ PASSED ] 28 tests.
[ FAILED ] 2 tests, listed below:
[ FAILED ] BarTest.ReturnsTrueOnSuccess
[ FAILED ] AnotherTest.DoesXyz
2 FAILED TESTS You can set the `GTEST_COLOR` environment variable or the `--gtest_color` command line flag to `yes`, `no`, or `auto` (the default) to enable colors, disable colors, or let googletest decide. When the value is `auto`, googletest will use colors if and only if the output goes to a terminal and (on non-Windows platforms) the `TERM` environment variable is set to `xterm` or `xterm-color`. **Availability**: Linux, Windows, Mac. #### Suppressing the Elapsed Time By default, googletest prints the time it takes to run each test. To disable that, run the test program with the `--gtest_print_time=0` command line flag, or set the GTEST_PRINT_TIME environment variable to `0`. **Availability**: Linux, Windows, Mac. #### Suppressing UTF-8 Text Output In case of assertion failures, googletest prints expected and actual values of type `string` both as hex-encoded strings as well as in readable UTF-8 text if they contain valid non-ASCII UTF-8 characters. If you want to suppress the UTF-8 text because, for example, you don't have an UTF-8 compatible output medium, run the test program with `--gtest_print_utf8=0` or set the `GTEST_PRINT_UTF8` environment variable to `0`. **Availability**: Linux, Windows, Mac. #### Generating an XML Report googletest can emit a detailed XML report to a file in addition to its normal textual output. The report contains the duration of each test, and thus can help you identify slow tests. The report is also used by the http://unittest dashboard to show per-test-method error messages. To generate the XML report, set the `GTEST_OUTPUT` environment variable or the `--gtest_output` flag to the string `"xml:path_to_output_file"`, which will create the file at the given location. You can also just use the string `"xml"`, in which case the output can be found in the `test_detail.xml` file in the current directory. If you specify a directory (for example, `"xml:output/directory/"` on Linux or `"xml:output\directory\"` on Windows), googletest will create the XML file in that directory, named after the test executable (e.g. `foo_test.xml` for test program `foo_test` or `foo_test.exe`). If the file already exists (perhaps left over from a previous run), googletest will pick a different name (e.g. `foo_test_1.xml`) to avoid overwriting it. The report is based on the `junitreport` Ant task. Since that format was originally intended for Java, a little interpretation is required to make it apply to googletest tests, as shown here: ```xml ``` * The root `` element corresponds to the entire test program. * `` elements correspond to googletest test suites. * `` elements correspond to googletest test functions. For instance, the following program ```c++ TEST(MathTest, Addition) { ... } TEST(MathTest, Subtraction) { ... } TEST(LogicTest, NonContradiction) { ... } ``` could generate this report: ```xml ... ... ``` Things to note: * The `tests` attribute of a `` or `` element tells how many test functions the googletest program or test suite contains, while the `failures` attribute tells how many of them failed. * The `time` attribute expresses the duration of the test, test suite, or entire test program in seconds. * The `timestamp` attribute records the local date and time of the test execution. * Each `` element corresponds to a single failed googletest assertion. **Availability**: Linux, Windows, Mac. #### Generating an JSON Report googletest can also emit a JSON report as an alternative format to XML. To generate the JSON report, set the `GTEST_OUTPUT` environment variable or the `--gtest_output` flag to the string `"json:path_to_output_file"`, which will create the file at the given location. You can also just use the string `"json"`, in which case the output can be found in the `test_detail.json` file in the current directory. The report format conforms to the following JSON Schema: ```json { "$schema": "http://json-schema.org/schema#", "type": "object", "definitions": { "Testsuite": { "type": "object", "properties": { "name": { "type": "string" }, "tests": { "type": "integer" }, "failures": { "type": "integer" }, "disabled": { "type": "integer" }, "time": { "type": "string" }, "testsuite": { "type": "array", "items": { "$ref": "#/definitions/TestInfo" } } } }, "TestInfo": { "type": "object", "properties": { "name": { "type": "string" }, "status": { "type": "string", "enum": ["RUN", "NOTRUN"] }, "time": { "type": "string" }, "classname": { "type": "string" }, "failures": { "type": "array", "items": { "$ref": "#/definitions/Failure" } } } }, "Failure": { "type": "object", "properties": { "failures": { "type": "string" }, "type": { "type": "string" } } } }, "properties": { "tests": { "type": "integer" }, "failures": { "type": "integer" }, "disabled": { "type": "integer" }, "errors": { "type": "integer" }, "timestamp": { "type": "string", "format": "date-time" }, "time": { "type": "string" }, "name": { "type": "string" }, "testsuites": { "type": "array", "items": { "$ref": "#/definitions/Testsuite" } } } } ``` The report uses the format that conforms to the following Proto3 using the [JSON encoding](https://developers.google.com/protocol-buffers/docs/proto3#json): ```proto syntax = "proto3"; package googletest; import "google/protobuf/timestamp.proto"; import "google/protobuf/duration.proto"; message UnitTest { int32 tests = 1; int32 failures = 2; int32 disabled = 3; int32 errors = 4; google.protobuf.Timestamp timestamp = 5; google.protobuf.Duration time = 6; string name = 7; repeated Testsuite testsuites = 8; } message TestCase { string name = 1; int32 tests = 2; int32 failures = 3; int32 disabled = 4; int32 errors = 5; google.protobuf.Duration time = 6; repeated TestInfo testsuite = 7; } message TestInfo { string name = 1; enum Status { RUN = 0; NOTRUN = 1; } Status status = 2; google.protobuf.Duration time = 3; string classname = 4; message Failure { string failures = 1; string type = 2; } repeated Failure failures = 5; } ``` For instance, the following program ```c++ TEST(MathTest, Addition) { ... } TEST(MathTest, Subtraction) { ... } TEST(LogicTest, NonContradiction) { ... } ``` could generate this report: ```json { "tests": 3, "failures": 1, "errors": 0, "time": "0.035s", "timestamp": "2011-10-31T18:52:42Z", "name": "AllTests", "testsuites": [ { "name": "MathTest", "tests": 2, "failures": 1, "errors": 0, "time": "0.015s", "testsuite": [ { "name": "Addition", "status": "RUN", "time": "0.007s", "classname": "", "failures": [ { "message": "Value of: add(1, 1)\n Actual: 3\nExpected: 2", "type": "" }, { "message": "Value of: add(1, -1)\n Actual: 1\nExpected: 0", "type": "" } ] }, { "name": "Subtraction", "status": "RUN", "time": "0.005s", "classname": "" } ] }, { "name": "LogicTest", "tests": 1, "failures": 0, "errors": 0, "time": "0.005s", "testsuite": [ { "name": "NonContradiction", "status": "RUN", "time": "0.005s", "classname": "" } ] } ] } ``` IMPORTANT: The exact format of the JSON document is subject to change. **Availability**: Linux, Windows, Mac. ### Controlling How Failures Are Reported #### Turning Assertion Failures into Break-Points When running test programs under a debugger, it's very convenient if the debugger can catch an assertion failure and automatically drop into interactive mode. googletest's *break-on-failure* mode supports this behavior. To enable it, set the `GTEST_BREAK_ON_FAILURE` environment variable to a value other than `0` . Alternatively, you can use the `--gtest_break_on_failure` command line flag. **Availability**: Linux, Windows, Mac. #### Disabling Catching Test-Thrown Exceptions googletest can be used either with or without exceptions enabled. If a test throws a C++ exception or (on Windows) a structured exception (SEH), by default googletest catches it, reports it as a test failure, and continues with the next test method. This maximizes the coverage of a test run. Also, on Windows an uncaught exception will cause a pop-up window, so catching the exceptions allows you to run the tests automatically. When debugging the test failures, however, you may instead want the exceptions to be handled by the debugger, such that you can examine the call stack when an exception is thrown. To achieve that, set the `GTEST_CATCH_EXCEPTIONS` environment variable to `0`, or use the `--gtest_catch_exceptions=0` flag when running the tests. **Availability**: Linux, Windows, Mac.