3 You can find recipes for using Google Mock here. If you haven't yet,
4 please read the [ForDummies](ForDummies.md) document first to make sure you understand
7 **Note:** Google Mock lives in the `testing` name space. For
8 readability, it is recommended to write `using ::testing::Foo;` once in
9 your file before using the name `Foo` defined by Google Mock. We omit
10 such `using` statements in this page for brevity, but you should do it
13 # Creating Mock Classes #
15 ## Mocking Private or Protected Methods ##
17 You must always put a mock method definition (`MOCK_METHOD*`) in a
18 `public:` section of the mock class, regardless of the method being
19 mocked being `public`, `protected`, or `private` in the base class.
20 This allows `ON_CALL` and `EXPECT_CALL` to reference the mock function
21 from outside of the mock class. (Yes, C++ allows a subclass to specify
22 a different access level than the base class on a virtual function.)
29 virtual bool Transform(Gadget* g) = 0;
32 virtual void Resume();
35 virtual int GetTimeOut();
38 class MockFoo : public Foo {
41 MOCK_METHOD1(Transform, bool(Gadget* g));
43 // The following must be in the public section, even though the
44 // methods are protected or private in the base class.
45 MOCK_METHOD0(Resume, void());
46 MOCK_METHOD0(GetTimeOut, int());
50 ## Mocking Overloaded Methods ##
52 You can mock overloaded functions as usual. No special attention is required:
58 // Must be virtual as we'll inherit from Foo.
61 // Overloaded on the types and/or numbers of arguments.
62 virtual int Add(Element x);
63 virtual int Add(int times, Element x);
65 // Overloaded on the const-ness of this object.
66 virtual Bar& GetBar();
67 virtual const Bar& GetBar() const;
70 class MockFoo : public Foo {
72 MOCK_METHOD1(Add, int(Element x));
73 MOCK_METHOD2(Add, int(int times, Element x);
75 MOCK_METHOD0(GetBar, Bar&());
76 MOCK_CONST_METHOD0(GetBar, const Bar&());
80 **Note:** if you don't mock all versions of the overloaded method, the
81 compiler will give you a warning about some methods in the base class
82 being hidden. To fix that, use `using` to bring them in scope:
85 class MockFoo : public Foo {
88 MOCK_METHOD1(Add, int(Element x));
89 // We don't want to mock int Add(int times, Element x);
94 ## Mocking Class Templates ##
96 To mock a class template, append `_T` to the `MOCK_*` macros:
99 template <typename Elem>
100 class StackInterface {
102 // Must be virtual as we'll inherit from StackInterface.
103 virtual ~StackInterface();
105 virtual int GetSize() const = 0;
106 virtual void Push(const Elem& x) = 0;
109 template <typename Elem>
110 class MockStack : public StackInterface<Elem> {
112 MOCK_CONST_METHOD0_T(GetSize, int());
113 MOCK_METHOD1_T(Push, void(const Elem& x));
117 ## Mocking Nonvirtual Methods ##
119 Google Mock can mock non-virtual functions to be used in what we call _hi-perf
120 dependency injection_.
122 In this case, instead of sharing a common base class with the real
123 class, your mock class will be _unrelated_ to the real class, but
124 contain methods with the same signatures. The syntax for mocking
125 non-virtual methods is the _same_ as mocking virtual methods:
128 // A simple packet stream class. None of its members is virtual.
129 class ConcretePacketStream {
131 void AppendPacket(Packet* new_packet);
132 const Packet* GetPacket(size_t packet_number) const;
133 size_t NumberOfPackets() const;
137 // A mock packet stream class. It inherits from no other, but defines
138 // GetPacket() and NumberOfPackets().
139 class MockPacketStream {
141 MOCK_CONST_METHOD1(GetPacket, const Packet*(size_t packet_number));
142 MOCK_CONST_METHOD0(NumberOfPackets, size_t());
147 Note that the mock class doesn't define `AppendPacket()`, unlike the
148 real class. That's fine as long as the test doesn't need to call it.
150 Next, you need a way to say that you want to use
151 `ConcretePacketStream` in production code and to use `MockPacketStream`
152 in tests. Since the functions are not virtual and the two classes are
153 unrelated, you must specify your choice at _compile time_ (as opposed
156 One way to do it is to templatize your code that needs to use a packet
157 stream. More specifically, you will give your code a template type
158 argument for the type of the packet stream. In production, you will
159 instantiate your template with `ConcretePacketStream` as the type
160 argument. In tests, you will instantiate the same template with
161 `MockPacketStream`. For example, you may write:
164 template <class PacketStream>
165 void CreateConnection(PacketStream* stream) { ... }
167 template <class PacketStream>
170 void ReadPackets(PacketStream* stream, size_t packet_num);
174 Then you can use `CreateConnection<ConcretePacketStream>()` and
175 `PacketReader<ConcretePacketStream>` in production code, and use
176 `CreateConnection<MockPacketStream>()` and
177 `PacketReader<MockPacketStream>` in tests.
180 MockPacketStream mock_stream;
181 EXPECT_CALL(mock_stream, ...)...;
182 .. set more expectations on mock_stream ...
183 PacketReader<MockPacketStream> reader(&mock_stream);
184 ... exercise reader ...
187 ## Mocking Free Functions ##
189 It's possible to use Google Mock to mock a free function (i.e. a
190 C-style function or a static method). You just need to rewrite your
191 code to use an interface (abstract class).
193 Instead of calling a free function (say, `OpenFile`) directly,
194 introduce an interface for it and have a concrete subclass that calls
198 class FileInterface {
201 virtual bool Open(const char* path, const char* mode) = 0;
204 class File : public FileInterface {
207 virtual bool Open(const char* path, const char* mode) {
208 return OpenFile(path, mode);
213 Your code should talk to `FileInterface` to open a file. Now it's
214 easy to mock out the function.
216 This may seem much hassle, but in practice you often have multiple
217 related functions that you can put in the same interface, so the
218 per-function syntactic overhead will be much lower.
220 If you are concerned about the performance overhead incurred by
221 virtual functions, and profiling confirms your concern, you can
222 combine this with the recipe for [mocking non-virtual methods](#mocking-nonvirtual-methods).
224 ## The Nice, the Strict, and the Naggy ##
226 If a mock method has no `EXPECT_CALL` spec but is called, Google Mock
227 will print a warning about the "uninteresting call". The rationale is:
229 * 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.
230 * However, this may also mean there's a bug in the test, so Google Mock shouldn't be silent either. If the user believes these calls are harmless, they can add an `EXPECT_CALL()` to suppress the warning.
232 However, sometimes you may want to suppress all "uninteresting call"
233 warnings, while sometimes you may want the opposite, i.e. to treat all
234 of them as errors. Google Mock lets you make the decision on a
235 per-mock-object basis.
237 Suppose your test uses a mock class `MockFoo`:
242 EXPECT_CALL(mock_foo, DoThis());
243 ... code that uses mock_foo ...
247 If a method of `mock_foo` other than `DoThis()` is called, it will be
248 reported by Google Mock as a warning. However, if you rewrite your
249 test to use `NiceMock<MockFoo>` instead, the warning will be gone,
250 resulting in a cleaner test output:
253 using ::testing::NiceMock;
256 NiceMock<MockFoo> mock_foo;
257 EXPECT_CALL(mock_foo, DoThis());
258 ... code that uses mock_foo ...
262 `NiceMock<MockFoo>` is a subclass of `MockFoo`, so it can be used
263 wherever `MockFoo` is accepted.
265 It also works if `MockFoo`'s constructor takes some arguments, as
266 `NiceMock<MockFoo>` "inherits" `MockFoo`'s constructors:
269 using ::testing::NiceMock;
272 NiceMock<MockFoo> mock_foo(5, "hi"); // Calls MockFoo(5, "hi").
273 EXPECT_CALL(mock_foo, DoThis());
274 ... code that uses mock_foo ...
278 The usage of `StrictMock` is similar, except that it makes all
279 uninteresting calls failures:
282 using ::testing::StrictMock;
285 StrictMock<MockFoo> mock_foo;
286 EXPECT_CALL(mock_foo, DoThis());
287 ... code that uses mock_foo ...
289 // The test will fail if a method of mock_foo other than DoThis()
294 There are some caveats though (I don't like them just as much as the
295 next guy, but sadly they are side effects of C++'s limitations):
297 1. `NiceMock<MockFoo>` and `StrictMock<MockFoo>` 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<StrictMock<MockFoo> >`) is **not** supported.
298 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).
299 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.)
301 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.
303 ## Simplifying the Interface without Breaking Existing Code ##
305 Sometimes a method has a long list of arguments that is mostly
306 uninteresting. For example,
312 virtual void send(LogSeverity severity, const char* full_filename,
313 const char* base_filename, int line,
314 const struct tm* tm_time,
315 const char* message, size_t message_len) = 0;
319 This method's argument list is lengthy and hard to work with (let's
320 say that the `message` argument is not even 0-terminated). If we mock
321 it as is, using the mock will be awkward. If, however, we try to
322 simplify this interface, we'll need to fix all clients depending on
323 it, which is often infeasible.
325 The trick is to re-dispatch the method in the mock class:
328 class ScopedMockLog : public LogSink {
331 virtual void send(LogSeverity severity, const char* full_filename,
332 const char* base_filename, int line, const tm* tm_time,
333 const char* message, size_t message_len) {
334 // We are only interested in the log severity, full file name, and
336 Log(severity, full_filename, std::string(message, message_len));
339 // Implements the mock method:
341 // void Log(LogSeverity severity,
342 // const string& file_path,
343 // const string& message);
344 MOCK_METHOD3(Log, void(LogSeverity severity, const string& file_path,
345 const string& message));
349 By defining a new mock method with a trimmed argument list, we make
350 the mock class much more user-friendly.
352 ## Alternative to Mocking Concrete Classes ##
354 Often you may find yourself using classes that don't implement
355 interfaces. In order to test your code that uses such a class (let's
356 call it `Concrete`), you may be tempted to make the methods of
357 `Concrete` virtual and then mock it.
361 Making a non-virtual function virtual is a big decision. It creates an
362 extension point where subclasses can tweak your class' behavior. This
363 weakens your control on the class because now it's harder to maintain
364 the class' invariants. You should make a function virtual only when
365 there is a valid reason for a subclass to override it.
367 Mocking concrete classes directly is problematic as it creates a tight
368 coupling between the class and the tests - any small change in the
369 class may invalidate your tests and make test maintenance a pain.
371 To avoid such problems, many programmers have been practicing "coding
372 to interfaces": instead of talking to the `Concrete` class, your code
373 would define an interface and talk to it. Then you implement that
374 interface as an adaptor on top of `Concrete`. In tests, you can easily
375 mock that interface to observe how your code is doing.
377 This technique incurs some overhead:
379 * You pay the cost of virtual function calls (usually not a problem).
380 * There is more abstraction for the programmers to learn.
382 However, it can also bring significant benefits in addition to better
385 * `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.
386 * 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.
388 Some people worry that if everyone is practicing this technique, they
389 will end up writing lots of redundant code. This concern is totally
390 understandable. However, there are two reasons why it may not be the
393 * 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.
394 * 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.
396 You need to weigh the pros and cons carefully for your particular
397 problem, but I'd like to assure you that the Java community has been
398 practicing this for a long time and it's a proven effective technique
399 applicable in a wide variety of situations. :-)
401 ## Delegating Calls to a Fake ##
403 Some times you have a non-trivial fake implementation of an
404 interface. For example:
410 virtual char DoThis(int n) = 0;
411 virtual void DoThat(const char* s, int* p) = 0;
414 class FakeFoo : public Foo {
416 virtual char DoThis(int n) {
417 return (n > 0) ? '+' :
421 virtual void DoThat(const char* s, int* p) {
427 Now you want to mock this interface such that you can set expectations
428 on it. However, you also want to use `FakeFoo` for the default
429 behavior, as duplicating it in the mock object is, well, a lot of
432 When you define the mock class using Google Mock, you can have it
433 delegate its default action to a fake class you already have, using
438 using ::testing::Invoke;
440 class MockFoo : public Foo {
442 // Normal mock method definitions using Google Mock.
443 MOCK_METHOD1(DoThis, char(int n));
444 MOCK_METHOD2(DoThat, void(const char* s, int* p));
446 // Delegates the default actions of the methods to a FakeFoo object.
447 // This must be called *before* the custom ON_CALL() statements.
448 void DelegateToFake() {
449 ON_CALL(*this, DoThis(_))
450 .WillByDefault(Invoke(&fake_, &FakeFoo::DoThis));
451 ON_CALL(*this, DoThat(_, _))
452 .WillByDefault(Invoke(&fake_, &FakeFoo::DoThat));
455 FakeFoo fake_; // Keeps an instance of the fake in the mock.
459 With that, you can use `MockFoo` in your tests as usual. Just remember
460 that if you don't explicitly set an action in an `ON_CALL()` or
461 `EXPECT_CALL()`, the fake will be called upon to do it:
468 foo.DelegateToFake(); // Enables the fake for delegation.
470 // Put your ON_CALL(foo, ...)s here, if any.
472 // No action specified, meaning to use the default action.
473 EXPECT_CALL(foo, DoThis(5));
474 EXPECT_CALL(foo, DoThat(_, _));
477 EXPECT_EQ('+', foo.DoThis(5)); // FakeFoo::DoThis() is invoked.
478 foo.DoThat("Hi", &n); // FakeFoo::DoThat() is invoked.
485 * If you want, you can still override the default action by providing your own `ON_CALL()` or using `.WillOnce()` / `.WillRepeatedly()` in `EXPECT_CALL()`.
486 * In `DelegateToFake()`, you only need to delegate the methods whose fake implementation you intend to use.
487 * 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<bool (FakeFoo::*)(double) const>(&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.).
488 * 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.
490 Regarding the tip on mixing a mock and a fake, here's an example on
491 why it may be a bad sign: Suppose you have a class `System` for
492 low-level system operations. In particular, it does file and I/O
493 operations. And suppose you want to test how your code uses `System`
494 to do I/O, and you just want the file operations to work normally. If
495 you mock out the entire `System` class, you'll have to provide a fake
496 implementation for the file operation part, which suggests that
497 `System` is taking on too many roles.
499 Instead, you can define a `FileOps` interface and an `IOOps` interface
500 and split `System`'s functionalities into the two. Then you can mock
501 `IOOps` without mocking `FileOps`.
503 ## Delegating Calls to a Real Object ##
505 When using testing doubles (mocks, fakes, stubs, and etc), sometimes
506 their behaviors will differ from those of the real objects. This
507 difference could be either intentional (as in simulating an error such
508 that you can test the error handling code) or unintentional. If your
509 mocks have different behaviors than the real objects by mistake, you
510 could end up with code that passes the tests but fails in production.
512 You can use the _delegating-to-real_ technique to ensure that your
513 mock has the same behavior as the real object while retaining the
514 ability to validate calls. This technique is very similar to the
515 delegating-to-fake technique, the difference being that we use a real
516 object instead of a fake. Here's an example:
520 using ::testing::AtLeast;
521 using ::testing::Invoke;
523 class MockFoo : public Foo {
526 // By default, all calls are delegated to the real object.
527 ON_CALL(*this, DoThis())
528 .WillByDefault(Invoke(&real_, &Foo::DoThis));
529 ON_CALL(*this, DoThat(_))
530 .WillByDefault(Invoke(&real_, &Foo::DoThat));
533 MOCK_METHOD0(DoThis, ...);
534 MOCK_METHOD1(DoThat, ...);
543 EXPECT_CALL(mock, DoThis())
545 EXPECT_CALL(mock, DoThat("Hi"))
547 ... use mock in test ...
550 With this, Google Mock will verify that your code made the right calls
551 (with the right arguments, in the right order, called the right number
552 of times, etc), and a real object will answer the calls (so the
553 behavior will be the same as in production). This gives you the best
556 ## Delegating Calls to a Parent Class ##
558 Ideally, you should code to interfaces, whose methods are all pure
559 virtual. In reality, sometimes you do need to mock a virtual method
560 that is not pure (i.e, it already has an implementation). For example:
567 virtual void Pure(int n) = 0;
568 virtual int Concrete(const char* str) { ... }
571 class MockFoo : public Foo {
573 // Mocking a pure method.
574 MOCK_METHOD1(Pure, void(int n));
575 // Mocking a concrete method. Foo::Concrete() is shadowed.
576 MOCK_METHOD1(Concrete, int(const char* str));
580 Sometimes you may want to call `Foo::Concrete()` instead of
581 `MockFoo::Concrete()`. Perhaps you want to do it as part of a stub
582 action, or perhaps your test doesn't need to mock `Concrete()` at all
583 (but it would be oh-so painful to have to define a new mock class
584 whenever you don't need to mock one of its methods).
586 The trick is to leave a back door in your mock class for accessing the
587 real methods in the base class:
590 class MockFoo : public Foo {
592 // Mocking a pure method.
593 MOCK_METHOD1(Pure, void(int n));
594 // Mocking a concrete method. Foo::Concrete() is shadowed.
595 MOCK_METHOD1(Concrete, int(const char* str));
597 // Use this to call Concrete() defined in Foo.
598 int FooConcrete(const char* str) { return Foo::Concrete(str); }
602 Now, you can call `Foo::Concrete()` inside an action by:
606 using ::testing::Invoke;
608 EXPECT_CALL(foo, Concrete(_))
609 .WillOnce(Invoke(&foo, &MockFoo::FooConcrete));
612 or tell the mock object that you don't want to mock `Concrete()`:
615 using ::testing::Invoke;
617 ON_CALL(foo, Concrete(_))
618 .WillByDefault(Invoke(&foo, &MockFoo::FooConcrete));
621 (Why don't we just write `Invoke(&foo, &Foo::Concrete)`? If you do
622 that, `MockFoo::Concrete()` will be called (and cause an infinite
623 recursion) since `Foo::Concrete()` is virtual. That's just how C++
628 ## Matching Argument Values Exactly ##
630 You can specify exactly which arguments a mock method is expecting:
633 using ::testing::Return;
635 EXPECT_CALL(foo, DoThis(5))
636 .WillOnce(Return('a'));
637 EXPECT_CALL(foo, DoThat("Hello", bar));
640 ## Using Simple Matchers ##
642 You can use matchers to match arguments that have a certain property:
646 using ::testing::NotNull;
647 using ::testing::Return;
649 EXPECT_CALL(foo, DoThis(Ge(5))) // The argument must be >= 5.
650 .WillOnce(Return('a'));
651 EXPECT_CALL(foo, DoThat("Hello", NotNull()));
652 // The second argument must not be NULL.
655 A frequently used matcher is `_`, which matches anything:
659 using ::testing::NotNull;
661 EXPECT_CALL(foo, DoThat(_, NotNull()));
664 ## Combining Matchers ##
666 You can build complex matchers from existing ones using `AllOf()`,
667 `AnyOf()`, and `Not()`:
670 using ::testing::AllOf;
672 using ::testing::HasSubstr;
674 using ::testing::Not;
676 // The argument must be > 5 and != 10.
677 EXPECT_CALL(foo, DoThis(AllOf(Gt(5),
680 // The first argument must not contain sub-string "blah".
681 EXPECT_CALL(foo, DoThat(Not(HasSubstr("blah")),
685 ## Casting Matchers ##
687 Google Mock matchers are statically typed, meaning that the compiler
688 can catch your mistake if you use a matcher of the wrong type (for
689 example, if you use `Eq(5)` to match a `string` argument). Good for
692 Sometimes, however, you know what you're doing and want the compiler
693 to give you some slack. One example is that you have a matcher for
694 `long` and the argument you want to match is `int`. While the two
695 types aren't exactly the same, there is nothing really wrong with
696 using a `Matcher<long>` to match an `int` - after all, we can first
697 convert the `int` argument to a `long` before giving it to the
700 To support this need, Google Mock gives you the
701 `SafeMatcherCast<T>(m)` function. It casts a matcher `m` to type
702 `Matcher<T>`. To ensure safety, Google Mock checks that (let `U` be the
705 1. Type `T` can be implicitly cast to type `U`;
706 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
707 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).
709 The code won't compile if any of these conditions aren't met.
714 using ::testing::SafeMatcherCast;
716 // A base class and a child class.
718 class Derived : public Base { ... };
720 class MockFoo : public Foo {
722 MOCK_METHOD1(DoThis, void(Derived* derived));
727 // m is a Matcher<Base*> we got from somewhere.
728 EXPECT_CALL(foo, DoThis(SafeMatcherCast<Derived*>(m)));
731 If you find `SafeMatcherCast<T>(m)` too limiting, you can use a similar
732 function `MatcherCast<T>(m)`. The difference is that `MatcherCast` works
733 as long as you can `static_cast` type `T` to type `U`.
735 `MatcherCast` essentially lets you bypass C++'s type system
736 (`static_cast` isn't always safe as it could throw away information,
737 for example), so be careful not to misuse/abuse it.
739 ## Selecting Between Overloaded Functions ##
741 If you expect an overloaded function to be called, the compiler may
742 need some help on which overloaded version it is.
744 To disambiguate functions overloaded on the const-ness of this object,
745 use the `Const()` argument wrapper.
748 using ::testing::ReturnRef;
750 class MockFoo : public Foo {
752 MOCK_METHOD0(GetBar, Bar&());
753 MOCK_CONST_METHOD0(GetBar, const Bar&());
759 EXPECT_CALL(foo, GetBar()) // The non-const GetBar().
760 .WillOnce(ReturnRef(bar1));
761 EXPECT_CALL(Const(foo), GetBar()) // The const GetBar().
762 .WillOnce(ReturnRef(bar2));
765 (`Const()` is defined by Google Mock and returns a `const` reference
768 To disambiguate overloaded functions with the same number of arguments
769 but different argument types, you may need to specify the exact type
770 of a matcher, either by wrapping your matcher in `Matcher<type>()`, or
771 using a matcher whose type is fixed (`TypedEq<type>`, `An<type>()`,
777 using ::testing::Matcher;
778 using ::testing::TypedEq;
780 class MockPrinter : public Printer {
782 MOCK_METHOD1(Print, void(int n));
783 MOCK_METHOD1(Print, void(char c));
786 TEST(PrinterTest, Print) {
789 EXPECT_CALL(printer, Print(An<int>())); // void Print(int);
790 EXPECT_CALL(printer, Print(Matcher<int>(Lt(5)))); // void Print(int);
791 EXPECT_CALL(printer, Print(TypedEq<char>('a'))); // void Print(char);
799 ## Performing Different Actions Based on the Arguments ##
801 When a mock method is called, the _last_ matching expectation that's
802 still active will be selected (think "newer overrides older"). So, you
803 can make a method do different things depending on its argument values
809 using ::testing::Return;
812 EXPECT_CALL(foo, DoThis(_))
813 .WillRepeatedly(Return('b'));
815 // The more specific case.
816 EXPECT_CALL(foo, DoThis(Lt(5)))
817 .WillRepeatedly(Return('a'));
820 Now, if `foo.DoThis()` is called with a value less than 5, `'a'` will
821 be returned; otherwise `'b'` will be returned.
823 ## Matching Multiple Arguments as a Whole ##
825 Sometimes it's not enough to match the arguments individually. For
826 example, we may want to say that the first argument must be less than
827 the second argument. The `With()` clause allows us to match
828 all arguments of a mock function as a whole. For example,
835 EXPECT_CALL(foo, InRange(Ne(0), _))
839 says that the first argument of `InRange()` must not be 0, and must be
840 less than the second argument.
842 The expression inside `With()` must be a matcher of type
843 `Matcher< ::testing::tuple<A1, ..., An> >`, where `A1`, ..., `An` are the
844 types of the function arguments.
846 You can also write `AllArgs(m)` instead of `m` inside `.With()`. The
847 two forms are equivalent, but `.With(AllArgs(Lt()))` is more readable
850 You can use `Args<k1, ..., kn>(m)` to match the `n` selected arguments
851 (as a tuple) against `m`. For example,
855 using ::testing::AllOf;
856 using ::testing::Args;
859 EXPECT_CALL(foo, Blah(_, _, _))
860 .With(AllOf(Args<0, 1>(Lt()), Args<1, 2>(Lt())));
863 says that `Blah()` will be called with arguments `x`, `y`, and `z` where
866 As a convenience and example, Google Mock provides some matchers for
867 2-tuples, including the `Lt()` matcher above. See the [CheatSheet](CheatSheet.md) for
870 Note that if you want to pass the arguments to a predicate of your own
871 (e.g. `.With(Args<0, 1>(Truly(&MyPredicate)))`), that predicate MUST be
872 written to take a `::testing::tuple` as its argument; Google Mock will pass the `n` selected arguments as _one_ single tuple to the predicate.
874 ## Using Matchers as Predicates ##
876 Have you noticed that a matcher is just a fancy predicate that also
877 knows how to describe itself? Many existing algorithms take predicates
878 as arguments (e.g. those defined in STL's `<algorithm>` header), and
879 it would be a shame if Google Mock matchers are not allowed to
882 Luckily, you can use a matcher where a unary predicate functor is
883 expected by wrapping it inside the `Matches()` function. For example,
891 // How many elements in v are >= 10?
892 const int count = count_if(v.begin(), v.end(), Matches(Ge(10)));
895 Since you can build complex matchers from simpler ones easily using
896 Google Mock, this gives you a way to conveniently construct composite
897 predicates (doing the same using STL's `<functional>` header is just
898 painful). For example, here's a predicate that's satisfied by any
899 number that is >= 0, <= 100, and != 50:
902 Matches(AllOf(Ge(0), Le(100), Ne(50)))
905 ## Using Matchers in Google Test Assertions ##
907 Since matchers are basically predicates that also know how to describe
908 themselves, there is a way to take advantage of them in
909 [Google Test](../../googletest/) assertions. It's
910 called `ASSERT_THAT` and `EXPECT_THAT`:
913 ASSERT_THAT(value, matcher); // Asserts that value matches matcher.
914 EXPECT_THAT(value, matcher); // The non-fatal version.
917 For example, in a Google Test test you can write:
920 #include "gmock/gmock.h"
922 using ::testing::AllOf;
925 using ::testing::MatchesRegex;
926 using ::testing::StartsWith;
929 EXPECT_THAT(Foo(), StartsWith("Hello"));
930 EXPECT_THAT(Bar(), MatchesRegex("Line \\d+"));
931 ASSERT_THAT(Baz(), AllOf(Ge(5), Le(10)));
934 which (as you can probably guess) executes `Foo()`, `Bar()`, and
935 `Baz()`, and verifies that:
937 * `Foo()` returns a string that starts with `"Hello"`.
938 * `Bar()` returns a string that matches regular expression `"Line \\d+"`.
939 * `Baz()` returns a number in the range [5, 10].
941 The nice thing about these macros is that _they read like
942 English_. They generate informative messages too. For example, if the
943 first `EXPECT_THAT()` above fails, the message will be something like:
948 Expected: starts with "Hello"
951 **Credit:** The idea of `(ASSERT|EXPECT)_THAT` was stolen from the
952 [Hamcrest](https://github.com/hamcrest/) project, which adds
953 `assertThat()` to JUnit.
955 ## Using Predicates as Matchers ##
957 Google Mock provides a built-in set of matchers. In case you find them
958 lacking, you can use an arbitray unary predicate function or functor
959 as a matcher - as long as the predicate accepts a value of the type
960 you want. You do this by wrapping the predicate inside the `Truly()`
961 function, for example:
964 using ::testing::Truly;
966 int IsEven(int n) { return (n % 2) == 0 ? 1 : 0; }
969 // Bar() must be called with an even number.
970 EXPECT_CALL(foo, Bar(Truly(IsEven)));
973 Note that the predicate function / functor doesn't have to return
974 `bool`. It works as long as the return value can be used as the
975 condition in statement `if (condition) ...`.
977 ## Matching Arguments that Are Not Copyable ##
979 When you do an `EXPECT_CALL(mock_obj, Foo(bar))`, Google Mock saves
980 away a copy of `bar`. When `Foo()` is called later, Google Mock
981 compares the argument to `Foo()` with the saved copy of `bar`. This
982 way, you don't need to worry about `bar` being modified or destroyed
983 after the `EXPECT_CALL()` is executed. The same is true when you use
984 matchers like `Eq(bar)`, `Le(bar)`, and so on.
986 But what if `bar` cannot be copied (i.e. has no copy constructor)? You
987 could define your own matcher function and use it with `Truly()`, as
988 the previous couple of recipes have shown. Or, you may be able to get
989 away from it if you can guarantee that `bar` won't be changed after
990 the `EXPECT_CALL()` is executed. Just tell Google Mock that it should
991 save a reference to `bar`, instead of a copy of it. Here's how:
995 using ::testing::ByRef;
998 // Expects that Foo()'s argument == bar.
999 EXPECT_CALL(mock_obj, Foo(Eq(ByRef(bar))));
1001 // Expects that Foo()'s argument < bar.
1002 EXPECT_CALL(mock_obj, Foo(Lt(ByRef(bar))));
1005 Remember: if you do this, don't change `bar` after the
1006 `EXPECT_CALL()`, or the result is undefined.
1008 ## Validating a Member of an Object ##
1010 Often a mock function takes a reference to object as an argument. When
1011 matching the argument, you may not want to compare the entire object
1012 against a fixed object, as that may be over-specification. Instead,
1013 you may need to validate a certain member variable or the result of a
1014 certain getter method of the object. You can do this with `Field()`
1015 and `Property()`. More specifically,
1021 is a matcher that matches a `Foo` object whose `bar` member variable
1022 satisfies matcher `m`.
1025 Property(&Foo::baz, m)
1028 is a matcher that matches a `Foo` object whose `baz()` method returns
1029 a value that satisfies matcher `m`.
1033 | Expression | Description |
1034 |:-----------------------------|:-----------------------------------|
1035 | `Field(&Foo::number, Ge(3))` | Matches `x` where `x.number >= 3`. |
1036 | `Property(&Foo::name, StartsWith("John "))` | Matches `x` where `x.name()` starts with `"John "`. |
1038 Note that in `Property(&Foo::baz, ...)`, method `baz()` must take no
1039 argument and be declared as `const`.
1041 BTW, `Field()` and `Property()` can also match plain pointers to
1042 objects. For instance,
1045 Field(&Foo::number, Ge(3))
1048 matches a plain pointer `p` where `p->number >= 3`. If `p` is `NULL`,
1049 the match will always fail regardless of the inner matcher.
1051 What if you want to validate more than one members at the same time?
1052 Remember that there is `AllOf()`.
1054 ## Validating the Value Pointed to by a Pointer Argument ##
1056 C++ functions often take pointers as arguments. You can use matchers
1057 like `IsNull()`, `NotNull()`, and other comparison matchers to match a
1058 pointer, but what if you want to make sure the value _pointed to_ by
1059 the pointer, instead of the pointer itself, has a certain property?
1060 Well, you can use the `Pointee(m)` matcher.
1062 `Pointee(m)` matches a pointer iff `m` matches the value the pointer
1063 points to. For example:
1066 using ::testing::Ge;
1067 using ::testing::Pointee;
1069 EXPECT_CALL(foo, Bar(Pointee(Ge(3))));
1072 expects `foo.Bar()` to be called with a pointer that points to a value
1073 greater than or equal to 3.
1075 One nice thing about `Pointee()` is that it treats a `NULL` pointer as
1076 a match failure, so you can write `Pointee(m)` instead of
1079 AllOf(NotNull(), Pointee(m))
1082 without worrying that a `NULL` pointer will crash your test.
1084 Also, did we tell you that `Pointee()` works with both raw pointers
1085 **and** smart pointers (`linked_ptr`, `shared_ptr`, `scoped_ptr`, and
1088 What if you have a pointer to pointer? You guessed it - you can use
1089 nested `Pointee()` to probe deeper inside the value. For example,
1090 `Pointee(Pointee(Lt(3)))` matches a pointer that points to a pointer
1091 that points to a number less than 3 (what a mouthful...).
1093 ## Testing a Certain Property of an Object ##
1095 Sometimes you want to specify that an object argument has a certain
1096 property, but there is no existing matcher that does this. If you want
1097 good error messages, you should define a matcher. If you want to do it
1098 quick and dirty, you could get away with writing an ordinary function.
1100 Let's say you have a mock function that takes an object of type `Foo`,
1101 which has an `int bar()` method and an `int baz()` method, and you
1102 want to constrain that the argument's `bar()` value plus its `baz()`
1103 value is a given number. Here's how you can define a matcher to do it:
1106 using ::testing::MatcherInterface;
1107 using ::testing::MatchResultListener;
1109 class BarPlusBazEqMatcher : public MatcherInterface<const Foo&> {
1111 explicit BarPlusBazEqMatcher(int expected_sum)
1112 : expected_sum_(expected_sum) {}
1114 virtual bool MatchAndExplain(const Foo& foo,
1115 MatchResultListener* listener) const {
1116 return (foo.bar() + foo.baz()) == expected_sum_;
1119 virtual void DescribeTo(::std::ostream* os) const {
1120 *os << "bar() + baz() equals " << expected_sum_;
1123 virtual void DescribeNegationTo(::std::ostream* os) const {
1124 *os << "bar() + baz() does not equal " << expected_sum_;
1127 const int expected_sum_;
1130 inline Matcher<const Foo&> BarPlusBazEq(int expected_sum) {
1131 return MakeMatcher(new BarPlusBazEqMatcher(expected_sum));
1136 EXPECT_CALL(..., DoThis(BarPlusBazEq(5)))...;
1139 ## Matching Containers ##
1141 Sometimes an STL container (e.g. list, vector, map, ...) is passed to
1142 a mock function and you may want to validate it. Since most STL
1143 containers support the `==` operator, you can write
1144 `Eq(expected_container)` or simply `expected_container` to match a
1147 Sometimes, though, you may want to be more flexible (for example, the
1148 first element must be an exact match, but the second element can be
1149 any positive number, and so on). Also, containers used in tests often
1150 have a small number of elements, and having to define the expected
1151 container out-of-line is a bit of a hassle.
1153 You can use the `ElementsAre()` or `UnorderedElementsAre()` matcher in
1158 using ::testing::ElementsAre;
1159 using ::testing::Gt;
1162 MOCK_METHOD1(Foo, void(const vector<int>& numbers));
1165 EXPECT_CALL(mock, Foo(ElementsAre(1, Gt(0), _, 5)));
1168 The above matcher says that the container must have 4 elements, which
1169 must be 1, greater than 0, anything, and 5 respectively.
1171 If you instead write:
1175 using ::testing::Gt;
1176 using ::testing::UnorderedElementsAre;
1179 MOCK_METHOD1(Foo, void(const vector<int>& numbers));
1182 EXPECT_CALL(mock, Foo(UnorderedElementsAre(1, Gt(0), _, 5)));
1185 It means that the container must have 4 elements, which under some
1186 permutation must be 1, greater than 0, anything, and 5 respectively.
1188 `ElementsAre()` and `UnorderedElementsAre()` are overloaded to take 0
1189 to 10 arguments. If more are needed, you can place them in a C-style
1190 array and use `ElementsAreArray()` or `UnorderedElementsAreArray()`
1194 using ::testing::ElementsAreArray;
1197 // ElementsAreArray accepts an array of element values.
1198 const int expected_vector1[] = { 1, 5, 2, 4, ... };
1199 EXPECT_CALL(mock, Foo(ElementsAreArray(expected_vector1)));
1201 // Or, an array of element matchers.
1202 Matcher<int> expected_vector2 = { 1, Gt(2), _, 3, ... };
1203 EXPECT_CALL(mock, Foo(ElementsAreArray(expected_vector2)));
1206 In case the array needs to be dynamically created (and therefore the
1207 array size cannot be inferred by the compiler), you can give
1208 `ElementsAreArray()` an additional argument to specify the array size:
1211 using ::testing::ElementsAreArray;
1213 int* const expected_vector3 = new int[count];
1214 ... fill expected_vector3 with values ...
1215 EXPECT_CALL(mock, Foo(ElementsAreArray(expected_vector3, count)));
1220 * `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.
1221 * You can use nested `ElementsAre*()` to match nested (multi-dimensional) containers.
1222 * If the container is passed by pointer instead of by reference, just write `Pointee(ElementsAre*(...))`.
1223 * The order of elements _matters_ for `ElementsAre*()`. Therefore don't use it with containers whose element order is undefined (e.g. `hash_map`).
1225 ## Sharing Matchers ##
1227 Under the hood, a Google Mock matcher object consists of a pointer to
1228 a ref-counted implementation object. Copying matchers is allowed and
1229 very efficient, as only the pointer is copied. When the last matcher
1230 that references the implementation object dies, the implementation
1231 object will be deleted.
1233 Therefore, if you have some complex matcher that you want to use again
1234 and again, there is no need to build it every time. Just assign it to a
1235 matcher variable and use that variable repeatedly! For example,
1238 Matcher<int> in_range = AllOf(Gt(5), Le(10));
1239 ... use in_range as a matcher in multiple EXPECT_CALLs ...
1242 # Setting Expectations #
1244 ## Knowing When to Expect ##
1246 `ON_CALL` is likely the single most under-utilized construct in Google Mock.
1248 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).
1250 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.
1252 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?
1254 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.
1256 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.
1258 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).
1260 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.
1262 ## Ignoring Uninteresting Calls ##
1264 If you are not interested in how a mock method is called, just don't
1265 say anything about it. In this case, if the method is ever called,
1266 Google Mock will perform its default action to allow the test program
1267 to continue. If you are not happy with the default action taken by
1268 Google Mock, you can override it using `DefaultValue<T>::Set()`
1269 (described later in this document) or `ON_CALL()`.
1271 Please note that once you expressed interest in a particular mock
1272 method (via `EXPECT_CALL()`), all invocations to it must match some
1273 expectation. If this function is called but the arguments don't match
1274 any `EXPECT_CALL()` statement, it will be an error.
1276 ## Disallowing Unexpected Calls ##
1278 If a mock method shouldn't be called at all, explicitly say so:
1283 EXPECT_CALL(foo, Bar(_))
1287 If some calls to the method are allowed, but the rest are not, just
1288 list all the expected calls:
1291 using ::testing::AnyNumber;
1292 using ::testing::Gt;
1294 EXPECT_CALL(foo, Bar(5));
1295 EXPECT_CALL(foo, Bar(Gt(10)))
1296 .Times(AnyNumber());
1299 A call to `foo.Bar()` that doesn't match any of the `EXPECT_CALL()`
1300 statements will be an error.
1302 ## Understanding Uninteresting vs Unexpected Calls ##
1304 _Uninteresting_ calls and _unexpected_ calls are different concepts in Google Mock. _Very_ different.
1306 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.
1308 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.
1310 **An unexpected call is always an error,** as the code under test doesn't behave the way the test expects it to behave.
1312 **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).
1314 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?
1316 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.
1318 A **strict mock** turns uninteresting call warnings into errors. So making a mock strict may change the test's result.
1320 Let's look at an example:
1324 NiceMock<MockDomainRegistry> mock_registry;
1325 EXPECT_CALL(mock_registry, GetDomainOwner("google.com"))
1326 .WillRepeatedly(Return("Larry Page"));
1328 // Use mock_registry in code under test.
1329 ... &mock_registry ...
1333 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.
1335 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`:
1338 EXPECT_CALL(mock_registry, GetDomainOwner(_))
1339 .Times(AnyNumber()); // catches all other calls to this method.
1340 EXPECT_CALL(mock_registry, GetDomainOwner("google.com"))
1341 .WillRepeatedly(Return("Larry Page"));
1344 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.
1346 Note that the order of the two `EXPECT_CALLs` is important, as a newer `EXPECT_CALL` takes precedence over an older one.
1348 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).
1350 ## Expecting Ordered Calls ##
1352 Although an `EXPECT_CALL()` statement defined earlier takes precedence
1353 when Google Mock tries to match a function call with an expectation,
1354 by default calls don't have to happen in the order `EXPECT_CALL()`
1355 statements are written. For example, if the arguments match the
1356 matchers in the third `EXPECT_CALL()`, but not those in the first two,
1357 then the third expectation will be used.
1359 If you would rather have all calls occur in the order of the
1360 expectations, put the `EXPECT_CALL()` statements in a block where you
1361 define a variable of type `InSequence`:
1365 using ::testing::InSequence;
1370 EXPECT_CALL(foo, DoThis(5));
1371 EXPECT_CALL(bar, DoThat(_))
1373 EXPECT_CALL(foo, DoThis(6));
1377 In this example, we expect a call to `foo.DoThis(5)`, followed by two
1378 calls to `bar.DoThat()` where the argument can be anything, which are
1379 in turn followed by a call to `foo.DoThis(6)`. If a call occurred
1380 out-of-order, Google Mock will report an error.
1382 ## Expecting Partially Ordered Calls ##
1384 Sometimes requiring everything to occur in a predetermined order can
1385 lead to brittle tests. For example, we may care about `A` occurring
1386 before both `B` and `C`, but aren't interested in the relative order
1387 of `B` and `C`. In this case, the test should reflect our real intent,
1388 instead of being overly constraining.
1390 Google Mock allows you to impose an arbitrary DAG (directed acyclic
1391 graph) on the calls. One way to express the DAG is to use the
1392 [After](CheatSheet.md#the-after-clause) clause of `EXPECT_CALL`.
1394 Another way is via the `InSequence()` clause (not the same as the
1395 `InSequence` class), which we borrowed from jMock 2. It's less
1396 flexible than `After()`, but more convenient when you have long chains
1397 of sequential calls, as it doesn't require you to come up with
1398 different names for the expectations in the chains. Here's how it
1401 If we view `EXPECT_CALL()` statements as nodes in a graph, and add an
1402 edge from node A to node B wherever A must occur before B, we can get
1403 a DAG. We use the term "sequence" to mean a directed path in this
1404 DAG. Now, if we decompose the DAG into sequences, we just need to know
1405 which sequences each `EXPECT_CALL()` belongs to in order to be able to
1406 reconstruct the original DAG.
1408 So, to specify the partial order on the expectations we need to do two
1409 things: first to define some `Sequence` objects, and then for each
1410 `EXPECT_CALL()` say which `Sequence` objects it is part
1411 of. Expectations in the same sequence must occur in the order they are
1412 written. For example,
1415 using ::testing::Sequence;
1419 EXPECT_CALL(foo, A())
1420 .InSequence(s1, s2);
1421 EXPECT_CALL(bar, B())
1423 EXPECT_CALL(bar, C())
1425 EXPECT_CALL(foo, D())
1429 specifies the following DAG (where `s1` is `A -> B`, and `s2` is `A ->
1440 This means that A must occur before B and C, and C must occur before
1441 D. There's no restriction about the order other than these.
1443 ## Controlling When an Expectation Retires ##
1445 When a mock method is called, Google Mock only consider expectations
1446 that are still active. An expectation is active when created, and
1447 becomes inactive (aka _retires_) when a call that has to occur later
1448 has occurred. For example, in
1452 using ::testing::Sequence;
1456 EXPECT_CALL(log, Log(WARNING, _, "File too large.")) // #1
1458 .InSequence(s1, s2);
1459 EXPECT_CALL(log, Log(WARNING, _, "Data set is empty.")) // #2
1461 EXPECT_CALL(log, Log(WARNING, _, "User not found.")) // #3
1465 as soon as either #2 or #3 is matched, #1 will retire. If a warning
1466 `"File too large."` is logged after this, it will be an error.
1468 Note that an expectation doesn't retire automatically when it's
1469 saturated. For example,
1474 EXPECT_CALL(log, Log(WARNING, _, _)); // #1
1475 EXPECT_CALL(log, Log(WARNING, _, "File too large.")); // #2
1478 says that there will be exactly one warning with the message `"File
1479 too large."`. If the second warning contains this message too, #2 will
1480 match again and result in an upper-bound-violated error.
1482 If this is not what you want, you can ask an expectation to retire as
1483 soon as it becomes saturated:
1488 EXPECT_CALL(log, Log(WARNING, _, _)); // #1
1489 EXPECT_CALL(log, Log(WARNING, _, "File too large.")) // #2
1490 .RetiresOnSaturation();
1493 Here #2 can be used only once, so if you have two warnings with the
1494 message `"File too large."`, the first will match #2 and the second
1495 will match #1 - there will be no error.
1499 ## Returning References from Mock Methods ##
1501 If a mock function's return type is a reference, you need to use
1502 `ReturnRef()` instead of `Return()` to return a result:
1505 using ::testing::ReturnRef;
1507 class MockFoo : public Foo {
1509 MOCK_METHOD0(GetBar, Bar&());
1515 EXPECT_CALL(foo, GetBar())
1516 .WillOnce(ReturnRef(bar));
1519 ## Returning Live Values from Mock Methods ##
1521 The `Return(x)` action saves a copy of `x` when the action is
1522 _created_, and always returns the same value whenever it's
1523 executed. Sometimes you may want to instead return the _live_ value of
1524 `x` (i.e. its value at the time when the action is _executed_.).
1526 If the mock function's return type is a reference, you can do it using
1527 `ReturnRef(x)`, as shown in the previous recipe ("Returning References
1528 from Mock Methods"). However, Google Mock doesn't let you use
1529 `ReturnRef()` in a mock function whose return type is not a reference,
1530 as doing that usually indicates a user error. So, what shall you do?
1532 You may be tempted to try `ByRef()`:
1535 using testing::ByRef;
1536 using testing::Return;
1538 class MockFoo : public Foo {
1540 MOCK_METHOD0(GetValue, int());
1545 EXPECT_CALL(foo, GetValue())
1546 .WillRepeatedly(Return(ByRef(x)));
1548 EXPECT_EQ(42, foo.GetValue());
1551 Unfortunately, it doesn't work here. The above code will fail with error:
1554 Value of: foo.GetValue()
1559 The reason is that `Return(value)` converts `value` to the actual
1560 return type of the mock function at the time when the action is
1561 _created_, not when it is _executed_. (This behavior was chosen for
1562 the action to be safe when `value` is a proxy object that references
1563 some temporary objects.) As a result, `ByRef(x)` is converted to an
1564 `int` value (instead of a `const int&`) when the expectation is set,
1565 and `Return(ByRef(x))` will always return 0.
1567 `ReturnPointee(pointer)` was provided to solve this problem
1568 specifically. It returns the value pointed to by `pointer` at the time
1569 the action is _executed_:
1572 using testing::ReturnPointee;
1576 EXPECT_CALL(foo, GetValue())
1577 .WillRepeatedly(ReturnPointee(&x)); // Note the & here.
1579 EXPECT_EQ(42, foo.GetValue()); // This will succeed now.
1582 ## Combining Actions ##
1584 Want to do more than one thing when a function is called? That's
1585 fine. `DoAll()` allow you to do sequence of actions every time. Only
1586 the return value of the last action in the sequence will be used.
1589 using ::testing::DoAll;
1591 class MockFoo : public Foo {
1593 MOCK_METHOD1(Bar, bool(int n));
1597 EXPECT_CALL(foo, Bar(_))
1598 .WillOnce(DoAll(action_1,
1604 ## Mocking Side Effects ##
1606 Sometimes a method exhibits its effect not via returning a value but
1607 via side effects. For example, it may change some global state or
1608 modify an output argument. To mock side effects, in general you can
1609 define your own action by implementing `::testing::ActionInterface`.
1611 If all you need to do is to change an output argument, the built-in
1612 `SetArgPointee()` action is convenient:
1615 using ::testing::SetArgPointee;
1617 class MockMutator : public Mutator {
1619 MOCK_METHOD2(Mutate, void(bool mutate, int* value));
1624 MockMutator mutator;
1625 EXPECT_CALL(mutator, Mutate(true, _))
1626 .WillOnce(SetArgPointee<1>(5));
1629 In this example, when `mutator.Mutate()` is called, we will assign 5
1630 to the `int` variable pointed to by argument #1
1633 `SetArgPointee()` conveniently makes an internal copy of the
1634 value you pass to it, removing the need to keep the value in scope and
1635 alive. The implication however is that the value must have a copy
1636 constructor and assignment operator.
1638 If the mock method also needs to return a value as well, you can chain
1639 `SetArgPointee()` with `Return()` using `DoAll()`:
1643 using ::testing::Return;
1644 using ::testing::SetArgPointee;
1646 class MockMutator : public Mutator {
1649 MOCK_METHOD1(MutateInt, bool(int* value));
1653 MockMutator mutator;
1654 EXPECT_CALL(mutator, MutateInt(_))
1655 .WillOnce(DoAll(SetArgPointee<0>(5),
1659 If the output argument is an array, use the
1660 `SetArrayArgument<N>(first, last)` action instead. It copies the
1661 elements in source range `[first, last)` to the array pointed to by
1662 the `N`-th (0-based) argument:
1665 using ::testing::NotNull;
1666 using ::testing::SetArrayArgument;
1668 class MockArrayMutator : public ArrayMutator {
1670 MOCK_METHOD2(Mutate, void(int* values, int num_values));
1675 MockArrayMutator mutator;
1676 int values[5] = { 1, 2, 3, 4, 5 };
1677 EXPECT_CALL(mutator, Mutate(NotNull(), 5))
1678 .WillOnce(SetArrayArgument<0>(values, values + 5));
1681 This also works when the argument is an output iterator:
1685 using ::testing::SetArrayArgument;
1687 class MockRolodex : public Rolodex {
1689 MOCK_METHOD1(GetNames, void(std::back_insert_iterator<vector<string> >));
1694 MockRolodex rolodex;
1695 vector<string> names;
1696 names.push_back("George");
1697 names.push_back("John");
1698 names.push_back("Thomas");
1699 EXPECT_CALL(rolodex, GetNames(_))
1700 .WillOnce(SetArrayArgument<0>(names.begin(), names.end()));
1703 ## Changing a Mock Object's Behavior Based on the State ##
1705 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:
1708 using ::testing::InSequence;
1709 using ::testing::Return;
1714 EXPECT_CALL(my_mock, IsDirty())
1715 .WillRepeatedly(Return(true));
1716 EXPECT_CALL(my_mock, Flush());
1717 EXPECT_CALL(my_mock, IsDirty())
1718 .WillRepeatedly(Return(false));
1720 my_mock.FlushIfDirty();
1723 This makes `my_mock.IsDirty()` return `true` before `my_mock.Flush()` is called and return `false` afterwards.
1725 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:
1729 using ::testing::SaveArg;
1730 using ::testing::Return;
1732 ACTION_P(ReturnPointee, p) { return *p; }
1734 int previous_value = 0;
1735 EXPECT_CALL(my_mock, GetPrevValue())
1736 .WillRepeatedly(ReturnPointee(&previous_value));
1737 EXPECT_CALL(my_mock, UpdateValue(_))
1738 .WillRepeatedly(SaveArg<0>(&previous_value));
1739 my_mock.DoSomethingToUpdateValue();
1742 Here `my_mock.GetPrevValue()` will always return the argument of the last `UpdateValue()` call.
1744 ## Setting the Default Value for a Return Type ##
1746 If a mock method's return type is a built-in C++ type or pointer, by
1747 default it will return 0 when invoked. Also, in C++ 11 and above, a mock
1748 method whose return type has a default constructor will return a default-constructed
1749 value by default. You only need to specify an
1750 action if this default value doesn't work for you.
1752 Sometimes, you may want to change this default value, or you may want
1753 to specify a default value for types Google Mock doesn't know
1754 about. You can do this using the `::testing::DefaultValue` class
1758 class MockFoo : public Foo {
1760 MOCK_METHOD0(CalculateBar, Bar());
1765 // Sets the default return value for type Bar.
1766 DefaultValue<Bar>::Set(default_bar);
1770 // We don't need to specify an action here, as the default
1771 // return value works for us.
1772 EXPECT_CALL(foo, CalculateBar());
1774 foo.CalculateBar(); // This should return default_bar.
1776 // Unsets the default return value.
1777 DefaultValue<Bar>::Clear();
1780 Please note that changing the default value for a type can make you
1781 tests hard to understand. We recommend you to use this feature
1782 judiciously. For example, you may want to make sure the `Set()` and
1783 `Clear()` calls are right next to the code that uses your mock.
1785 ## Setting the Default Actions for a Mock Method ##
1787 You've learned how to change the default value of a given
1788 type. However, this may be too coarse for your purpose: perhaps you
1789 have two mock methods with the same return type and you want them to
1790 have different behaviors. The `ON_CALL()` macro allows you to
1791 customize your mock's behavior at the method level:
1795 using ::testing::AnyNumber;
1796 using ::testing::Gt;
1797 using ::testing::Return;
1799 ON_CALL(foo, Sign(_))
1800 .WillByDefault(Return(-1));
1801 ON_CALL(foo, Sign(0))
1802 .WillByDefault(Return(0));
1803 ON_CALL(foo, Sign(Gt(0)))
1804 .WillByDefault(Return(1));
1806 EXPECT_CALL(foo, Sign(_))
1807 .Times(AnyNumber());
1809 foo.Sign(5); // This should return 1.
1810 foo.Sign(-9); // This should return -1.
1811 foo.Sign(0); // This should return 0.
1814 As you may have guessed, when there are more than one `ON_CALL()`
1815 statements, the news order take precedence over the older ones. In
1816 other words, the **last** one that matches the function arguments will
1817 be used. This matching order allows you to set up the common behavior
1818 in a mock object's constructor or the test fixture's set-up phase and
1819 specialize the mock's behavior later.
1821 ## Using Functions/Methods/Functors as Actions ##
1823 If the built-in actions don't suit you, you can easily use an existing
1824 function, method, or functor as an action:
1828 using ::testing::Invoke;
1830 class MockFoo : public Foo {
1832 MOCK_METHOD2(Sum, int(int x, int y));
1833 MOCK_METHOD1(ComplexJob, bool(int x));
1836 int CalculateSum(int x, int y) { return x + y; }
1840 bool ComplexJob(int x);
1846 EXPECT_CALL(foo, Sum(_, _))
1847 .WillOnce(Invoke(CalculateSum));
1848 EXPECT_CALL(foo, ComplexJob(_))
1849 .WillOnce(Invoke(&helper, &Helper::ComplexJob));
1851 foo.Sum(5, 6); // Invokes CalculateSum(5, 6).
1852 foo.ComplexJob(10); // Invokes helper.ComplexJob(10);
1855 The only requirement is that the type of the function, etc must be
1856 _compatible_ with the signature of the mock function, meaning that the
1857 latter's arguments can be implicitly converted to the corresponding
1858 arguments of the former, and the former's return type can be
1859 implicitly converted to that of the latter. So, you can invoke
1860 something whose type is _not_ exactly the same as the mock function,
1861 as long as it's safe to do so - nice, huh?
1863 ## Invoking a Function/Method/Functor Without Arguments ##
1865 `Invoke()` is very useful for doing actions that are more complex. It
1866 passes the mock function's arguments to the function or functor being
1867 invoked such that the callee has the full context of the call to work
1868 with. If the invoked function is not interested in some or all of the
1869 arguments, it can simply ignore them.
1871 Yet, a common pattern is that a test author wants to invoke a function
1872 without the arguments of the mock function. `Invoke()` allows her to
1873 do that using a wrapper function that throws away the arguments before
1874 invoking an underlining nullary function. Needless to say, this can be
1875 tedious and obscures the intent of the test.
1877 `InvokeWithoutArgs()` solves this problem. It's like `Invoke()` except
1878 that it doesn't pass the mock function's arguments to the
1879 callee. Here's an example:
1883 using ::testing::InvokeWithoutArgs;
1885 class MockFoo : public Foo {
1887 MOCK_METHOD1(ComplexJob, bool(int n));
1894 EXPECT_CALL(foo, ComplexJob(_))
1895 .WillOnce(InvokeWithoutArgs(Job1));
1897 foo.ComplexJob(10); // Invokes Job1().
1900 ## Invoking an Argument of the Mock Function ##
1902 Sometimes a mock function will receive a function pointer or a functor
1903 (in other words, a "callable") as an argument, e.g.
1906 class MockFoo : public Foo {
1908 MOCK_METHOD2(DoThis, bool(int n, bool (*fp)(int)));
1912 and you may want to invoke this callable argument:
1918 EXPECT_CALL(foo, DoThis(_, _))
1920 // Will execute (*fp)(5), where fp is the
1921 // second argument DoThis() receives.
1924 Arghh, you need to refer to a mock function argument but your version
1925 of C++ has no lambdas, so you have to define your own action. :-(
1928 Well, Google Mock has an action to solve _exactly_ this problem:
1931 InvokeArgument<N>(arg_1, arg_2, ..., arg_m)
1934 will invoke the `N`-th (0-based) argument the mock function receives,
1935 with `arg_1`, `arg_2`, ..., and `arg_m`. No matter if the argument is
1936 a function pointer or a functor, Google Mock handles them both.
1938 With that, you could write:
1942 using ::testing::InvokeArgument;
1944 EXPECT_CALL(foo, DoThis(_, _))
1945 .WillOnce(InvokeArgument<1>(5));
1946 // Will execute (*fp)(5), where fp is the
1947 // second argument DoThis() receives.
1950 What if the callable takes an argument by reference? No problem - just
1951 wrap it inside `ByRef()`:
1955 MOCK_METHOD1(Bar, bool(bool (*fp)(int, const Helper&)));
1958 using ::testing::ByRef;
1959 using ::testing::InvokeArgument;
1965 EXPECT_CALL(foo, Bar(_))
1966 .WillOnce(InvokeArgument<0>(5, ByRef(helper)));
1967 // ByRef(helper) guarantees that a reference to helper, not a copy of it,
1968 // will be passed to the callable.
1971 What if the callable takes an argument by reference and we do **not**
1972 wrap the argument in `ByRef()`? Then `InvokeArgument()` will _make a
1973 copy_ of the argument, and pass a _reference to the copy_, instead of
1974 a reference to the original value, to the callable. This is especially
1975 handy when the argument is a temporary value:
1979 MOCK_METHOD1(DoThat, bool(bool (*f)(const double& x, const string& s)));
1982 using ::testing::InvokeArgument;
1987 EXPECT_CALL(foo, DoThat(_))
1988 .WillOnce(InvokeArgument<0>(5.0, string("Hi")));
1989 // Will execute (*f)(5.0, string("Hi")), where f is the function pointer
1990 // DoThat() receives. Note that the values 5.0 and string("Hi") are
1991 // temporary and dead once the EXPECT_CALL() statement finishes. Yet
1992 // it's fine to perform this action later, since a copy of the values
1993 // are kept inside the InvokeArgument action.
1996 ## Ignoring an Action's Result ##
1998 Sometimes you have an action that returns _something_, but you need an
1999 action that returns `void` (perhaps you want to use it in a mock
2000 function that returns `void`, or perhaps it needs to be used in
2001 `DoAll()` and it's not the last in the list). `IgnoreResult()` lets
2002 you do that. For example:
2006 using ::testing::Invoke;
2007 using ::testing::Return;
2009 int Process(const MyData& data);
2010 string DoSomething();
2012 class MockFoo : public Foo {
2014 MOCK_METHOD1(Abc, void(const MyData& data));
2015 MOCK_METHOD0(Xyz, bool());
2020 EXPECT_CALL(foo, Abc(_))
2021 // .WillOnce(Invoke(Process));
2022 // The above line won't compile as Process() returns int but Abc() needs
2024 .WillOnce(IgnoreResult(Invoke(Process)));
2026 EXPECT_CALL(foo, Xyz())
2027 .WillOnce(DoAll(IgnoreResult(Invoke(DoSomething)),
2028 // Ignores the string DoSomething() returns.
2032 Note that you **cannot** use `IgnoreResult()` on an action that already
2033 returns `void`. Doing so will lead to ugly compiler errors.
2035 ## Selecting an Action's Arguments ##
2037 Say you have a mock function `Foo()` that takes seven arguments, and
2038 you have a custom action that you want to invoke when `Foo()` is
2039 called. Trouble is, the custom action only wants three arguments:
2043 using ::testing::Invoke;
2045 MOCK_METHOD7(Foo, bool(bool visible, const string& name, int x, int y,
2046 const map<pair<int, int>, double>& weight,
2047 double min_weight, double max_wight));
2050 bool IsVisibleInQuadrant1(bool visible, int x, int y) {
2051 return visible && x >= 0 && y >= 0;
2055 EXPECT_CALL(mock, Foo(_, _, _, _, _, _, _))
2056 .WillOnce(Invoke(IsVisibleInQuadrant1)); // Uh, won't compile. :-(
2059 To please the compiler God, you can to define an "adaptor" that has
2060 the same signature as `Foo()` and calls the custom action with the
2065 using ::testing::Invoke;
2067 bool MyIsVisibleInQuadrant1(bool visible, const string& name, int x, int y,
2068 const map<pair<int, int>, double>& weight,
2069 double min_weight, double max_wight) {
2070 return IsVisibleInQuadrant1(visible, x, y);
2074 EXPECT_CALL(mock, Foo(_, _, _, _, _, _, _))
2075 .WillOnce(Invoke(MyIsVisibleInQuadrant1)); // Now it works.
2078 But isn't this awkward?
2080 Google Mock provides a generic _action adaptor_, so you can spend your
2081 time minding more important business than writing your own
2082 adaptors. Here's the syntax:
2085 WithArgs<N1, N2, ..., Nk>(action)
2088 creates an action that passes the arguments of the mock function at
2089 the given indices (0-based) to the inner `action` and performs
2090 it. Using `WithArgs`, our original example can be written as:
2094 using ::testing::Invoke;
2095 using ::testing::WithArgs;
2097 EXPECT_CALL(mock, Foo(_, _, _, _, _, _, _))
2098 .WillOnce(WithArgs<0, 2, 3>(Invoke(IsVisibleInQuadrant1)));
2099 // No need to define your own adaptor.
2102 For better readability, Google Mock also gives you:
2104 * `WithoutArgs(action)` when the inner `action` takes _no_ argument, and
2105 * `WithArg<N>(action)` (no `s` after `Arg`) when the inner `action` takes _one_ argument.
2107 As you may have realized, `InvokeWithoutArgs(...)` is just syntactic
2108 sugar for `WithoutArgs(Invoke(...))`.
2112 * The inner action used in `WithArgs` and friends does not have to be `Invoke()` -- it can be anything.
2113 * You can repeat an argument in the argument list if necessary, e.g. `WithArgs<2, 3, 3, 5>(...)`.
2114 * You can change the order of the arguments, e.g. `WithArgs<3, 2, 1>(...)`.
2115 * 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.
2117 ## Ignoring Arguments in Action Functions ##
2119 The selecting-an-action's-arguments recipe showed us one way to make a
2120 mock function and an action with incompatible argument lists fit
2121 together. The downside is that wrapping the action in
2122 `WithArgs<...>()` can get tedious for people writing the tests.
2124 If you are defining a function, method, or functor to be used with
2125 `Invoke*()`, and you are not interested in some of its arguments, an
2126 alternative to `WithArgs` is to declare the uninteresting arguments as
2127 `Unused`. This makes the definition less cluttered and less fragile in
2128 case the types of the uninteresting arguments change. It could also
2129 increase the chance the action function can be reused. For example,
2133 MOCK_METHOD3(Foo, double(const string& label, double x, double y));
2134 MOCK_METHOD3(Bar, double(int index, double x, double y));
2141 using ::testing::Invoke;
2143 double DistanceToOriginWithLabel(const string& label, double x, double y) {
2144 return sqrt(x*x + y*y);
2147 double DistanceToOriginWithIndex(int index, double x, double y) {
2148 return sqrt(x*x + y*y);
2152 EXEPCT_CALL(mock, Foo("abc", _, _))
2153 .WillOnce(Invoke(DistanceToOriginWithLabel));
2154 EXEPCT_CALL(mock, Bar(5, _, _))
2155 .WillOnce(Invoke(DistanceToOriginWithIndex));
2162 using ::testing::Invoke;
2163 using ::testing::Unused;
2165 double DistanceToOrigin(Unused, double x, double y) {
2166 return sqrt(x*x + y*y);
2170 EXEPCT_CALL(mock, Foo("abc", _, _))
2171 .WillOnce(Invoke(DistanceToOrigin));
2172 EXEPCT_CALL(mock, Bar(5, _, _))
2173 .WillOnce(Invoke(DistanceToOrigin));
2176 ## Sharing Actions ##
2178 Just like matchers, a Google Mock action object consists of a pointer
2179 to a ref-counted implementation object. Therefore copying actions is
2180 also allowed and very efficient. When the last action that references
2181 the implementation object dies, the implementation object will be
2184 If you have some complex action that you want to use again and again,
2185 you may not have to build it from scratch every time. If the action
2186 doesn't have an internal state (i.e. if it always does the same thing
2187 no matter how many times it has been called), you can assign it to an
2188 action variable and use that variable repeatedly. For example:
2191 Action<bool(int*)> set_flag = DoAll(SetArgPointee<0>(5),
2193 ... use set_flag in .WillOnce() and .WillRepeatedly() ...
2196 However, if the action has its own state, you may be surprised if you
2197 share the action object. Suppose you have an action factory
2198 `IncrementCounter(init)` which creates an action that increments and
2199 returns a counter whose initial value is `init`, using two actions
2200 created from the same expression and using a shared action will
2201 exihibit different behaviors. Example:
2204 EXPECT_CALL(foo, DoThis())
2205 .WillRepeatedly(IncrementCounter(0));
2206 EXPECT_CALL(foo, DoThat())
2207 .WillRepeatedly(IncrementCounter(0));
2208 foo.DoThis(); // Returns 1.
2209 foo.DoThis(); // Returns 2.
2210 foo.DoThat(); // Returns 1 - Blah() uses a different
2211 // counter than Bar()'s.
2217 Action<int()> increment = IncrementCounter(0);
2219 EXPECT_CALL(foo, DoThis())
2220 .WillRepeatedly(increment);
2221 EXPECT_CALL(foo, DoThat())
2222 .WillRepeatedly(increment);
2223 foo.DoThis(); // Returns 1.
2224 foo.DoThis(); // Returns 2.
2225 foo.DoThat(); // Returns 3 - the counter is shared.
2228 # Misc Recipes on Using Google Mock #
2230 ## Mocking Methods That Use Move-Only Types ##
2232 C++11 introduced *move-only types*. A move-only-typed value can be moved from
2233 one object to another, but cannot be copied. `std::unique_ptr<T>` is
2234 probably the most commonly used move-only type.
2236 Mocking a method that takes and/or returns move-only types presents some
2237 challenges, but nothing insurmountable. This recipe shows you how you can do it.
2238 Note that the support for move-only method arguments was only introduced to
2239 gMock in April 2017; in older code, you may find more complex
2240 [workarounds](#LegacyMoveOnly) for lack of this feature.
2242 Let’s say we are working on a fictional project that lets one post and share
2243 snippets called “buzzes”. Your code uses these types:
2246 enum class AccessLevel { kInternal, kPublic };
2250 explicit Buzz(AccessLevel access) { ... }
2256 virtual ~Buzzer() {}
2257 virtual std::unique_ptr<Buzz> MakeBuzz(StringPiece text) = 0;
2258 virtual bool ShareBuzz(std::unique_ptr<Buzz> buzz, int64_t timestamp) = 0;
2263 A `Buzz` object represents a snippet being posted. A class that implements the
2264 `Buzzer` interface is capable of creating and sharing `Buzz`es. Methods in
2265 `Buzzer` may return a `unique_ptr<Buzz>` or take a
2266 `unique_ptr<Buzz>`. Now we need to mock `Buzzer` in our tests.
2268 To mock a method that accepts or returns move-only types, you just use the
2269 familiar `MOCK_METHOD` syntax as usual:
2272 class MockBuzzer : public Buzzer {
2274 MOCK_METHOD1(MakeBuzz, std::unique_ptr<Buzz>(StringPiece text));
2275 MOCK_METHOD2(ShareBuzz, bool(std::unique_ptr<Buzz> buzz, int64_t timestamp));
2279 Now that we have the mock class defined, we can use it in tests. In the
2280 following code examples, we assume that we have defined a `MockBuzzer` object
2281 named `mock_buzzer_`:
2284 MockBuzzer mock_buzzer_;
2287 First let’s see how we can set expectations on the `MakeBuzz()` method, which
2288 returns a `unique_ptr<Buzz>`.
2290 As usual, if you set an expectation without an action (i.e. the `.WillOnce()` or
2291 `.WillRepeated()` clause), when that expectation fires, the default action for
2292 that method will be taken. Since `unique_ptr<>` has a default constructor
2293 that returns a null `unique_ptr`, that’s what you’ll get if you don’t specify an
2297 // Use the default action.
2298 EXPECT_CALL(mock_buzzer_, MakeBuzz("hello"));
2300 // Triggers the previous EXPECT_CALL.
2301 EXPECT_EQ(nullptr, mock_buzzer_.MakeBuzz("hello"));
2304 If you are not happy with the default action, you can tweak it as usual; see
2305 [Setting Default Actions](#OnCall).
2307 If you just need to return a pre-defined move-only value, you can use the
2308 `Return(ByMove(...))` action:
2311 // When this fires, the unique_ptr<> specified by ByMove(...) will
2313 EXPECT_CALL(mock_buzzer_, MakeBuzz("world"))
2314 .WillOnce(Return(ByMove(MakeUnique<Buzz>(AccessLevel::kInternal))));
2316 EXPECT_NE(nullptr, mock_buzzer_.MakeBuzz("world"));
2319 Note that `ByMove()` is essential here - if you drop it, the code won’t compile.
2321 Quiz time! What do you think will happen if a `Return(ByMove(...))` action is
2322 performed more than once (e.g. you write
2323 `.WillRepeatedly(Return(ByMove(...)));`)? Come think of it, after the first
2324 time the action runs, the source value will be consumed (since it’s a move-only
2325 value), so the next time around, there’s no value to move from -- you’ll get a
2326 run-time error that `Return(ByMove(...))` can only be run once.
2328 If you need your mock method to do more than just moving a pre-defined value,
2329 remember that you can always use a lambda or a callable object, which can do
2330 pretty much anything you want:
2333 EXPECT_CALL(mock_buzzer_, MakeBuzz("x"))
2334 .WillRepeatedly([](StringPiece text) {
2335 return MakeUnique<Buzz>(AccessLevel::kInternal);
2338 EXPECT_NE(nullptr, mock_buzzer_.MakeBuzz("x"));
2339 EXPECT_NE(nullptr, mock_buzzer_.MakeBuzz("x"));
2342 Every time this `EXPECT_CALL` fires, a new `unique_ptr<Buzz>` will be
2343 created and returned. You cannot do this with `Return(ByMove(...))`.
2345 That covers returning move-only values; but how do we work with methods
2346 accepting move-only arguments? The answer is that they work normally, although
2347 some actions will not compile when any of method's arguments are move-only. You
2348 can always use `Return`, or a [lambda or functor](#FunctionsAsActions):
2351 using ::testing::Unused;
2353 EXPECT_CALL(mock_buzzer_, ShareBuzz(NotNull(), _)) .WillOnce(Return(true));
2354 EXPECT_TRUE(mock_buzzer_.ShareBuzz(MakeUnique<Buzz>(AccessLevel::kInternal)),
2357 EXPECT_CALL(mock_buzzer_, ShareBuzz(_, _)) .WillOnce(
2358 [](std::unique_ptr<Buzz> buzz, Unused) { return buzz != nullptr; });
2359 EXPECT_FALSE(mock_buzzer_.ShareBuzz(nullptr, 0));
2362 Many built-in actions (`WithArgs`, `WithoutArgs`,`DeleteArg`, `SaveArg`, ...)
2363 could in principle support move-only arguments, but the support for this is not
2364 implemented yet. If this is blocking you, please file a bug.
2366 A few actions (e.g. `DoAll`) copy their arguments internally, so they can never
2367 work with non-copyable objects; you'll have to use functors instead.
2369 ##### Legacy workarounds for move-only types {#LegacyMoveOnly}
2371 Support for move-only function arguments was only introduced to gMock in April
2372 2017. In older code, you may encounter the following workaround for the lack of
2373 this feature (it is no longer necessary - we're including it just for
2377 class MockBuzzer : public Buzzer {
2379 MOCK_METHOD2(DoShareBuzz, bool(Buzz* buzz, Time timestamp));
2380 bool ShareBuzz(std::unique_ptr<Buzz> buzz, Time timestamp) override {
2381 return DoShareBuzz(buzz.get(), timestamp);
2386 The trick is to delegate the `ShareBuzz()` method to a mock method (let’s call
2387 it `DoShareBuzz()`) that does not take move-only parameters. Then, instead of
2388 setting expectations on `ShareBuzz()`, you set them on the `DoShareBuzz()` mock
2392 MockBuzzer mock_buzzer_;
2393 EXPECT_CALL(mock_buzzer_, DoShareBuzz(NotNull(), _));
2395 // When one calls ShareBuzz() on the MockBuzzer like this, the call is
2396 // forwarded to DoShareBuzz(), which is mocked. Therefore this statement
2397 // will trigger the above EXPECT_CALL.
2398 mock_buzzer_.ShareBuzz(MakeUnique<Buzz>(AccessLevel::kInternal), 0);
2403 ## Making the Compilation Faster ##
2405 Believe it or not, the _vast majority_ of the time spent on compiling
2406 a mock class is in generating its constructor and destructor, as they
2407 perform non-trivial tasks (e.g. verification of the
2408 expectations). What's more, mock methods with different signatures
2409 have different types and thus their constructors/destructors need to
2410 be generated by the compiler separately. As a result, if you mock many
2411 different types of methods, compiling your mock class can get really
2414 If you are experiencing slow compilation, you can move the definition
2415 of your mock class' constructor and destructor out of the class body
2416 and into a `.cpp` file. This way, even if you `#include` your mock
2417 class in N files, the compiler only needs to generate its constructor
2418 and destructor once, resulting in a much faster compilation.
2420 Let's illustrate the idea using an example. Here's the definition of a
2421 mock class before applying this recipe:
2426 class MockFoo : public Foo {
2428 // Since we don't declare the constructor or the destructor,
2429 // the compiler will generate them in every translation unit
2430 // where this mock class is used.
2432 MOCK_METHOD0(DoThis, int());
2433 MOCK_METHOD1(DoThat, bool(const char* str));
2434 ... more mock methods ...
2438 After the change, it would look like:
2443 class MockFoo : public Foo {
2445 // The constructor and destructor are declared, but not defined, here.
2449 MOCK_METHOD0(DoThis, int());
2450 MOCK_METHOD1(DoThat, bool(const char* str));
2451 ... more mock methods ...
2456 // File mock_foo.cpp.
2457 #include "path/to/mock_foo.h"
2459 // The definitions may appear trivial, but the functions actually do a
2460 // lot of things through the constructors/destructors of the member
2461 // variables used to implement the mock methods.
2462 MockFoo::MockFoo() {}
2463 MockFoo::~MockFoo() {}
2466 ## Forcing a Verification ##
2468 When it's being destroyed, your friendly mock object will automatically
2469 verify that all expectations on it have been satisfied, and will
2470 generate [Google Test](../../googletest/) failures
2471 if not. This is convenient as it leaves you with one less thing to
2472 worry about. That is, unless you are not sure if your mock object will
2475 How could it be that your mock object won't eventually be destroyed?
2476 Well, it might be created on the heap and owned by the code you are
2477 testing. Suppose there's a bug in that code and it doesn't delete the
2478 mock object properly - you could end up with a passing test when
2479 there's actually a bug.
2481 Using a heap checker is a good idea and can alleviate the concern, but
2482 its implementation may not be 100% reliable. So, sometimes you do want
2483 to _force_ Google Mock to verify a mock object before it is
2484 (hopefully) destructed. You can do this with
2485 `Mock::VerifyAndClearExpectations(&mock_object)`:
2488 TEST(MyServerTest, ProcessesRequest) {
2489 using ::testing::Mock;
2491 MockFoo* const foo = new MockFoo;
2492 EXPECT_CALL(*foo, ...)...;
2493 // ... other expectations ...
2495 // server now owns foo.
2496 MyServer server(foo);
2497 server.ProcessRequest(...);
2499 // In case that server's destructor will forget to delete foo,
2500 // this will verify the expectations anyway.
2501 Mock::VerifyAndClearExpectations(foo);
2502 } // server is destroyed when it goes out of scope here.
2505 **Tip:** The `Mock::VerifyAndClearExpectations()` function returns a
2506 `bool` to indicate whether the verification was successful (`true` for
2507 yes), so you can wrap that function call inside a `ASSERT_TRUE()` if
2508 there is no point going further when the verification has failed.
2510 ## Using Check Points ##
2512 Sometimes you may want to "reset" a mock object at various check
2513 points in your test: at each check point, you verify that all existing
2514 expectations on the mock object have been satisfied, and then you set
2515 some new expectations on it as if it's newly created. This allows you
2516 to work with a mock object in "phases" whose sizes are each
2519 One such scenario is that in your test's `SetUp()` function, you may
2520 want to put the object you are testing into a certain state, with the
2521 help from a mock object. Once in the desired state, you want to clear
2522 all expectations on the mock, such that in the `TEST_F` body you can
2523 set fresh expectations on it.
2525 As you may have figured out, the `Mock::VerifyAndClearExpectations()`
2526 function we saw in the previous recipe can help you here. Or, if you
2527 are using `ON_CALL()` to set default actions on the mock object and
2528 want to clear the default actions as well, use
2529 `Mock::VerifyAndClear(&mock_object)` instead. This function does what
2530 `Mock::VerifyAndClearExpectations(&mock_object)` does and returns the
2531 same `bool`, **plus** it clears the `ON_CALL()` statements on
2534 Another trick you can use to achieve the same effect is to put the
2535 expectations in sequences and insert calls to a dummy "check-point"
2536 function at specific places. Then you can verify that the mock
2537 function calls do happen at the right time. For example, if you are
2546 and want to verify that `Foo(1)` and `Foo(3)` both invoke
2547 `mock.Bar("a")`, but `Foo(2)` doesn't invoke anything. You can write:
2550 using ::testing::MockFunction;
2552 TEST(FooTest, InvokesBarCorrectly) {
2554 // Class MockFunction<F> has exactly one mock method. It is named
2555 // Call() and has type F.
2556 MockFunction<void(string check_point_name)> check;
2560 EXPECT_CALL(mock, Bar("a"));
2561 EXPECT_CALL(check, Call("1"));
2562 EXPECT_CALL(check, Call("2"));
2563 EXPECT_CALL(mock, Bar("a"));
2573 The expectation spec says that the first `Bar("a")` must happen before
2574 check point "1", the second `Bar("a")` must happen after check point "2",
2575 and nothing should happen between the two check points. The explicit
2576 check points make it easy to tell which `Bar("a")` is called by which
2579 ## Mocking Destructors ##
2581 Sometimes you want to make sure a mock object is destructed at the
2582 right time, e.g. after `bar->A()` is called but before `bar->B()` is
2583 called. We already know that you can specify constraints on the order
2584 of mock function calls, so all we need to do is to mock the destructor
2585 of the mock function.
2587 This sounds simple, except for one problem: a destructor is a special
2588 function with special syntax and special semantics, and the
2589 `MOCK_METHOD0` macro doesn't work for it:
2592 MOCK_METHOD0(~MockFoo, void()); // Won't compile!
2595 The good news is that you can use a simple pattern to achieve the same
2596 effect. First, add a mock function `Die()` to your mock class and call
2597 it in the destructor, like this:
2600 class MockFoo : public Foo {
2602 // Add the following two lines to the mock class.
2603 MOCK_METHOD0(Die, void());
2604 virtual ~MockFoo() { Die(); }
2608 (If the name `Die()` clashes with an existing symbol, choose another
2609 name.) Now, we have translated the problem of testing when a `MockFoo`
2610 object dies to testing when its `Die()` method is called:
2613 MockFoo* foo = new MockFoo;
2614 MockBar* bar = new MockBar;
2619 // Expects *foo to die after bar->A() and before bar->B().
2620 EXPECT_CALL(*bar, A());
2621 EXPECT_CALL(*foo, Die());
2622 EXPECT_CALL(*bar, B());
2628 ## Using Google Mock and Threads ##
2630 **IMPORTANT NOTE:** What we describe in this recipe is **ONLY** true on
2631 platforms where Google Mock is thread-safe. Currently these are only
2632 platforms that support the pthreads library (this includes Linux and Mac).
2633 To make it thread-safe on other platforms we only need to implement
2634 some synchronization operations in `"gtest/internal/gtest-port.h"`.
2636 In a **unit** test, it's best if you could isolate and test a piece of
2637 code in a single-threaded context. That avoids race conditions and
2638 dead locks, and makes debugging your test much easier.
2640 Yet many programs are multi-threaded, and sometimes to test something
2641 we need to pound on it from more than one thread. Google Mock works
2642 for this purpose too.
2644 Remember the steps for using a mock:
2646 1. Create a mock object `foo`.
2647 1. Set its default actions and expectations using `ON_CALL()` and `EXPECT_CALL()`.
2648 1. The code under test calls methods of `foo`.
2649 1. Optionally, verify and reset the mock.
2650 1. Destroy the mock yourself, or let the code under test destroy it. The destructor will automatically verify it.
2652 If you follow the following simple rules, your mocks and threads can
2653 live happily together:
2655 * Execute your _test code_ (as opposed to the code being tested) in _one_ thread. This makes your test easy to follow.
2656 * Obviously, you can do step #1 without locking.
2657 * When doing step #2 and #5, make sure no other thread is accessing `foo`. Obvious too, huh?
2658 * #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.
2660 If you violate the rules (for example, if you set expectations on a
2661 mock while another thread is calling its methods), you get undefined
2662 behavior. That's not fun, so don't do it.
2664 Google Mock guarantees that the action for a mock function is done in
2665 the same thread that called the mock function. For example, in
2668 EXPECT_CALL(mock, Foo(1))
2670 EXPECT_CALL(mock, Foo(2))
2674 if `Foo(1)` is called in thread 1 and `Foo(2)` is called in thread 2,
2675 Google Mock will execute `action1` in thread 1 and `action2` in thread
2678 Google Mock does _not_ impose a sequence on actions performed in
2679 different threads (doing so may create deadlocks as the actions may
2680 need to cooperate). This means that the execution of `action1` and
2681 `action2` in the above example _may_ interleave. If this is a problem,
2682 you should add proper synchronization logic to `action1` and `action2`
2683 to make the test thread-safe.
2686 Also, remember that `DefaultValue<T>` is a global resource that
2687 potentially affects _all_ living mock objects in your
2688 program. Naturally, you won't want to mess with it from multiple
2689 threads or when there still are mocks in action.
2691 ## Controlling How Much Information Google Mock Prints ##
2693 When Google Mock sees something that has the potential of being an
2694 error (e.g. a mock function with no expectation is called, a.k.a. an
2695 uninteresting call, which is allowed but perhaps you forgot to
2696 explicitly ban the call), it prints some warning messages, including
2697 the arguments of the function and the return value. Hopefully this
2698 will remind you to take a look and see if there is indeed a problem.
2700 Sometimes you are confident that your tests are correct and may not
2701 appreciate such friendly messages. Some other times, you are debugging
2702 your tests or learning about the behavior of the code you are testing,
2703 and wish you could observe every mock call that happens (including
2704 argument values and the return value). Clearly, one size doesn't fit
2707 You can control how much Google Mock tells you using the
2708 `--gmock_verbose=LEVEL` command-line flag, where `LEVEL` is a string
2709 with three possible values:
2711 * `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.
2712 * `warning`: Google Mock will print both warnings and errors (less verbose). This is the default.
2713 * `error`: Google Mock will print errors only (least verbose).
2715 Alternatively, you can adjust the value of that flag from within your
2719 ::testing::FLAGS_gmock_verbose = "error";
2722 Now, judiciously use the right flag to enable Google Mock serve you better!
2724 ## Gaining Super Vision into Mock Calls ##
2726 You have a test using Google Mock. It fails: Google Mock tells you
2727 that some expectations aren't satisfied. However, you aren't sure why:
2728 Is there a typo somewhere in the matchers? Did you mess up the order
2729 of the `EXPECT_CALL`s? Or is the code under test doing something
2730 wrong? How can you find out the cause?
2732 Won't it be nice if you have X-ray vision and can actually see the
2733 trace of all `EXPECT_CALL`s and mock method calls as they are made?
2734 For each call, would you like to see its actual argument values and
2735 which `EXPECT_CALL` Google Mock thinks it matches?
2737 You can unlock this power by running your test with the
2738 `--gmock_verbose=info` flag. For example, given the test program:
2742 using testing::HasSubstr;
2743 using testing::Return;
2747 MOCK_METHOD2(F, void(const string& x, const string& y));
2752 EXPECT_CALL(mock, F(_, _)).WillRepeatedly(Return());
2753 EXPECT_CALL(mock, F("a", "b"));
2754 EXPECT_CALL(mock, F("c", HasSubstr("d")));
2756 mock.F("a", "good");
2761 if you run it with `--gmock_verbose=info`, you will see this output:
2766 foo_test.cc:14: EXPECT_CALL(mock, F(_, _)) invoked
2767 foo_test.cc:15: EXPECT_CALL(mock, F("a", "b")) invoked
2768 foo_test.cc:16: EXPECT_CALL(mock, F("c", HasSubstr("d"))) invoked
2769 foo_test.cc:14: Mock function call matches EXPECT_CALL(mock, F(_, _))...
2770 Function call: F(@0x7fff7c8dad40"a", @0x7fff7c8dad10"good")
2771 foo_test.cc:15: Mock function call matches EXPECT_CALL(mock, F("a", "b"))...
2772 Function call: F(@0x7fff7c8dada0"a", @0x7fff7c8dad70"b")
2773 foo_test.cc:16: Failure
2774 Actual function call count doesn't match EXPECT_CALL(mock, F("c", HasSubstr("d")))...
2775 Expected: to be called once
2776 Actual: never called - unsatisfied and active
2780 Suppose the bug is that the `"c"` in the third `EXPECT_CALL` is a typo
2781 and should actually be `"a"`. With the above message, you should see
2782 that the actual `F("a", "good")` call is matched by the first
2783 `EXPECT_CALL`, not the third as you thought. From that it should be
2784 obvious that the third `EXPECT_CALL` is written wrong. Case solved.
2786 ## Running Tests in Emacs ##
2788 If you build and run your tests in Emacs, the source file locations of
2789 Google Mock and [Google Test](../../googletest/)
2790 errors will be highlighted. Just press `<Enter>` on one of them and
2791 you'll be taken to the offending line. Or, you can just type `C-x ``
2792 to jump to the next error.
2794 To make it even easier, you can add the following lines to your
2798 (global-set-key "\M-m" 'compile) ; m is for make
2799 (global-set-key [M-down] 'next-error)
2800 (global-set-key [M-up] '(lambda () (interactive) (next-error -1)))
2803 Then you can type `M-m` to start a build, or `M-up`/`M-down` to move
2804 back and forth between errors.
2806 ## Fusing Google Mock Source Files ##
2808 Google Mock's implementation consists of dozens of files (excluding
2809 its own tests). Sometimes you may want them to be packaged up in
2810 fewer files instead, such that you can easily copy them to a new
2811 machine and start hacking there. For this we provide an experimental
2812 Python script `fuse_gmock_files.py` in the `scripts/` directory
2813 (starting with release 1.2.0). Assuming you have Python 2.4 or above
2814 installed on your machine, just go to that directory and run
2816 python fuse_gmock_files.py OUTPUT_DIR
2819 and you should see an `OUTPUT_DIR` directory being created with files
2820 `gtest/gtest.h`, `gmock/gmock.h`, and `gmock-gtest-all.cc` in it.
2821 These three files contain everything you need to use Google Mock (and
2822 Google Test). Just copy them to anywhere you want and you are ready
2823 to write tests and use mocks. You can use the
2824 [scrpts/test/Makefile](../scripts/test/Makefile) file as an example on how to compile your tests
2827 # Extending Google Mock #
2829 ## Writing New Matchers Quickly ##
2831 The `MATCHER*` family of macros can be used to define custom matchers
2835 MATCHER(name, description_string_expression) { statements; }
2838 will define a matcher with the given name that executes the
2839 statements, which must return a `bool` to indicate if the match
2840 succeeds. Inside the statements, you can refer to the value being
2841 matched by `arg`, and refer to its type by `arg_type`.
2843 The description string is a `string`-typed expression that documents
2844 what the matcher does, and is used to generate the failure message
2845 when the match fails. It can (and should) reference the special
2846 `bool` variable `negation`, and should evaluate to the description of
2847 the matcher when `negation` is `false`, or that of the matcher's
2848 negation when `negation` is `true`.
2850 For convenience, we allow the description string to be empty (`""`),
2851 in which case Google Mock will use the sequence of words in the
2852 matcher name as the description.
2856 MATCHER(IsDivisibleBy7, "") { return (arg % 7) == 0; }
2860 // Expects mock_foo.Bar(n) to be called where n is divisible by 7.
2861 EXPECT_CALL(mock_foo, Bar(IsDivisibleBy7()));
2865 using ::testing::Not;
2867 EXPECT_THAT(some_expression, IsDivisibleBy7());
2868 EXPECT_THAT(some_other_expression, Not(IsDivisibleBy7()));
2870 If the above assertions fail, they will print something like:
2872 Value of: some_expression
2873 Expected: is divisible by 7
2876 Value of: some_other_expression
2877 Expected: not (is divisible by 7)
2880 where the descriptions `"is divisible by 7"` and `"not (is divisible
2881 by 7)"` are automatically calculated from the matcher name
2884 As you may have noticed, the auto-generated descriptions (especially
2885 those for the negation) may not be so great. You can always override
2886 them with a string expression of your own:
2888 MATCHER(IsDivisibleBy7, std::string(negation ? "isn't" : "is") +
2889 " divisible by 7") {
2890 return (arg % 7) == 0;
2894 Optionally, you can stream additional information to a hidden argument
2895 named `result_listener` to explain the match result. For example, a
2896 better definition of `IsDivisibleBy7` is:
2898 MATCHER(IsDivisibleBy7, "") {
2902 *result_listener << "the remainder is " << (arg % 7);
2907 With this definition, the above assertion will give a better message:
2909 Value of: some_expression
2910 Expected: is divisible by 7
2911 Actual: 27 (the remainder is 6)
2914 You should let `MatchAndExplain()` print _any additional information_
2915 that can help a user understand the match result. Note that it should
2916 explain why the match succeeds in case of a success (unless it's
2917 obvious) - this is useful when the matcher is used inside
2918 `Not()`. There is no need to print the argument value itself, as
2919 Google Mock already prints it for you.
2923 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.
2924 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.
2926 ## Writing New Parameterized Matchers Quickly ##
2928 Sometimes you'll want to define a matcher that has parameters. For that you
2931 MATCHER_P(name, param_name, description_string) { statements; }
2933 where the description string can be either `""` or a string expression
2934 that references `negation` and `param_name`.
2938 MATCHER_P(HasAbsoluteValue, value, "") { return abs(arg) == value; }
2940 will allow you to write:
2942 EXPECT_THAT(Blah("a"), HasAbsoluteValue(n));
2944 which may lead to this message (assuming `n` is 10):
2947 Expected: has absolute value 10
2951 Note that both the matcher description and its parameter are
2952 printed, making the message human-friendly.
2954 In the matcher definition body, you can write `foo_type` to
2955 reference the type of a parameter named `foo`. For example, in the
2956 body of `MATCHER_P(HasAbsoluteValue, value)` above, you can write
2957 `value_type` to refer to the type of `value`.
2959 Google Mock also provides `MATCHER_P2`, `MATCHER_P3`, ..., up to
2960 `MATCHER_P10` to support multi-parameter matchers:
2962 MATCHER_Pk(name, param_1, ..., param_k, description_string) { statements; }
2965 Please note that the custom description string is for a particular
2966 **instance** of the matcher, where the parameters have been bound to
2967 actual values. Therefore usually you'll want the parameter values to
2968 be part of the description. Google Mock lets you do that by
2969 referencing the matcher parameters in the description string
2974 using ::testing::PrintToString;
2975 MATCHER_P2(InClosedRange, low, hi,
2976 std::string(negation ? "isn't" : "is") + " in range [" +
2977 PrintToString(low) + ", " + PrintToString(hi) + "]") {
2978 return low <= arg && arg <= hi;
2981 EXPECT_THAT(3, InClosedRange(4, 6));
2983 would generate a failure that contains the message:
2985 Expected: is in range [4, 6]
2988 If you specify `""` as the description, the failure message will
2989 contain the sequence of words in the matcher name followed by the
2990 parameter values printed as a tuple. For example,
2992 MATCHER_P2(InClosedRange, low, hi, "") { ... }
2994 EXPECT_THAT(3, InClosedRange(4, 6));
2996 would generate a failure that contains the text:
2998 Expected: in closed range (4, 6)
3001 For the purpose of typing, you can view
3003 MATCHER_Pk(Foo, p1, ..., pk, description_string) { ... }
3007 template <typename p1_type, ..., typename pk_type>
3008 FooMatcherPk<p1_type, ..., pk_type>
3009 Foo(p1_type p1, ..., pk_type pk) { ... }
3012 When you write `Foo(v1, ..., vk)`, the compiler infers the types of
3013 the parameters `v1`, ..., and `vk` for you. If you are not happy with
3014 the result of the type inference, you can specify the types by
3015 explicitly instantiating the template, as in `Foo<long, bool>(5, false)`.
3016 As said earlier, you don't get to (or need to) specify
3017 `arg_type` as that's determined by the context in which the matcher
3020 You can assign the result of expression `Foo(p1, ..., pk)` to a
3021 variable of type `FooMatcherPk<p1_type, ..., pk_type>`. This can be
3022 useful when composing matchers. Matchers that don't have a parameter
3023 or have only one parameter have special types: you can assign `Foo()`
3024 to a `FooMatcher`-typed variable, and assign `Foo(p)` to a
3025 `FooMatcherP<p_type>`-typed variable.
3027 While you can instantiate a matcher template with reference types,
3028 passing the parameters by pointer usually makes your code more
3029 readable. If, however, you still want to pass a parameter by
3030 reference, be aware that in the failure message generated by the
3031 matcher you will see the value of the referenced object but not its
3034 You can overload matchers with different numbers of parameters:
3036 MATCHER_P(Blah, a, description_string_1) { ... }
3037 MATCHER_P2(Blah, a, b, description_string_2) { ... }
3040 While it's tempting to always use the `MATCHER*` macros when defining
3041 a new matcher, you should also consider implementing
3042 `MatcherInterface` or using `MakePolymorphicMatcher()` instead (see
3043 the recipes that follow), especially if you need to use the matcher a
3044 lot. While these approaches require more work, they give you more
3045 control on the types of the value being matched and the matcher
3046 parameters, which in general leads to better compiler error messages
3047 that pay off in the long run. They also allow overloading matchers
3048 based on parameter types (as opposed to just based on the number of
3051 ## Writing New Monomorphic Matchers ##
3053 A matcher of argument type `T` implements
3054 `::testing::MatcherInterface<T>` and does two things: it tests whether a
3055 value of type `T` matches the matcher, and can describe what kind of
3056 values it matches. The latter ability is used for generating readable
3057 error messages when expectations are violated.
3059 The interface looks like this:
3062 class MatchResultListener {
3065 // Streams x to the underlying ostream; does nothing if the ostream
3067 template <typename T>
3068 MatchResultListener& operator<<(const T& x);
3070 // Returns the underlying ostream.
3071 ::std::ostream* stream();
3074 template <typename T>
3075 class MatcherInterface {
3077 virtual ~MatcherInterface();
3079 // Returns true iff the matcher matches x; also explains the match
3080 // result to 'listener'.
3081 virtual bool MatchAndExplain(T x, MatchResultListener* listener) const = 0;
3083 // Describes this matcher to an ostream.
3084 virtual void DescribeTo(::std::ostream* os) const = 0;
3086 // Describes the negation of this matcher to an ostream.
3087 virtual void DescribeNegationTo(::std::ostream* os) const;
3091 If you need a custom matcher but `Truly()` is not a good option (for
3092 example, you may not be happy with the way `Truly(predicate)`
3093 describes itself, or you may want your matcher to be polymorphic as
3094 `Eq(value)` is), you can define a matcher to do whatever you want in
3095 two steps: first implement the matcher interface, and then define a
3096 factory function to create a matcher instance. The second step is not
3097 strictly needed but it makes the syntax of using the matcher nicer.
3099 For example, you can define a matcher to test whether an `int` is
3100 divisible by 7 and then use it like this:
3102 using ::testing::MakeMatcher;
3103 using ::testing::Matcher;
3104 using ::testing::MatcherInterface;
3105 using ::testing::MatchResultListener;
3107 class DivisibleBy7Matcher : public MatcherInterface<int> {
3109 virtual bool MatchAndExplain(int n, MatchResultListener* listener) const {
3110 return (n % 7) == 0;
3113 virtual void DescribeTo(::std::ostream* os) const {
3114 *os << "is divisible by 7";
3117 virtual void DescribeNegationTo(::std::ostream* os) const {
3118 *os << "is not divisible by 7";
3122 inline Matcher<int> DivisibleBy7() {
3123 return MakeMatcher(new DivisibleBy7Matcher);
3127 EXPECT_CALL(foo, Bar(DivisibleBy7()));
3130 You may improve the matcher message by streaming additional
3131 information to the `listener` argument in `MatchAndExplain()`:
3134 class DivisibleBy7Matcher : public MatcherInterface<int> {
3136 virtual bool MatchAndExplain(int n,
3137 MatchResultListener* listener) const {
3138 const int remainder = n % 7;
3139 if (remainder != 0) {
3140 *listener << "the remainder is " << remainder;
3142 return remainder == 0;
3148 Then, `EXPECT_THAT(x, DivisibleBy7());` may general a message like this:
3151 Expected: is divisible by 7
3152 Actual: 23 (the remainder is 2)
3155 ## Writing New Polymorphic Matchers ##
3157 You've learned how to write your own matchers in the previous
3158 recipe. Just one problem: a matcher created using `MakeMatcher()` only
3159 works for one particular type of arguments. If you want a
3160 _polymorphic_ matcher that works with arguments of several types (for
3161 instance, `Eq(x)` can be used to match a `value` as long as `value` ==
3162 `x` compiles -- `value` and `x` don't have to share the same type),
3163 you can learn the trick from `"gmock/gmock-matchers.h"` but it's a bit
3166 Fortunately, most of the time you can define a polymorphic matcher
3167 easily with the help of `MakePolymorphicMatcher()`. Here's how you can
3168 define `NotNull()` as an example:
3171 using ::testing::MakePolymorphicMatcher;
3172 using ::testing::MatchResultListener;
3173 using ::testing::NotNull;
3174 using ::testing::PolymorphicMatcher;
3176 class NotNullMatcher {
3178 // To implement a polymorphic matcher, first define a COPYABLE class
3179 // that has three members MatchAndExplain(), DescribeTo(), and
3180 // DescribeNegationTo(), like the following.
3182 // In this example, we want to use NotNull() with any pointer, so
3183 // MatchAndExplain() accepts a pointer of any type as its first argument.
3184 // In general, you can define MatchAndExplain() as an ordinary method or
3185 // a method template, or even overload it.
3186 template <typename T>
3187 bool MatchAndExplain(T* p,
3188 MatchResultListener* /* listener */) const {
3192 // Describes the property of a value matching this matcher.
3193 void DescribeTo(::std::ostream* os) const { *os << "is not NULL"; }
3195 // Describes the property of a value NOT matching this matcher.
3196 void DescribeNegationTo(::std::ostream* os) const { *os << "is NULL"; }
3199 // To construct a polymorphic matcher, pass an instance of the class
3200 // to MakePolymorphicMatcher(). Note the return type.
3201 inline PolymorphicMatcher<NotNullMatcher> NotNull() {
3202 return MakePolymorphicMatcher(NotNullMatcher());
3206 EXPECT_CALL(foo, Bar(NotNull())); // The argument must be a non-NULL pointer.
3209 **Note:** Your polymorphic matcher class does **not** need to inherit from
3210 `MatcherInterface` or any other class, and its methods do **not** need
3213 Like in a monomorphic matcher, you may explain the match result by
3214 streaming additional information to the `listener` argument in
3215 `MatchAndExplain()`.
3217 ## Writing New Cardinalities ##
3219 A cardinality is used in `Times()` to tell Google Mock how many times
3220 you expect a call to occur. It doesn't have to be exact. For example,
3221 you can say `AtLeast(5)` or `Between(2, 4)`.
3223 If the built-in set of cardinalities doesn't suit you, you are free to
3224 define your own by implementing the following interface (in namespace
3228 class CardinalityInterface {
3230 virtual ~CardinalityInterface();
3232 // Returns true iff call_count calls will satisfy this cardinality.
3233 virtual bool IsSatisfiedByCallCount(int call_count) const = 0;
3235 // Returns true iff call_count calls will saturate this cardinality.
3236 virtual bool IsSaturatedByCallCount(int call_count) const = 0;
3238 // Describes self to an ostream.
3239 virtual void DescribeTo(::std::ostream* os) const = 0;
3243 For example, to specify that a call must occur even number of times,
3247 using ::testing::Cardinality;
3248 using ::testing::CardinalityInterface;
3249 using ::testing::MakeCardinality;
3251 class EvenNumberCardinality : public CardinalityInterface {
3253 virtual bool IsSatisfiedByCallCount(int call_count) const {
3254 return (call_count % 2) == 0;
3257 virtual bool IsSaturatedByCallCount(int call_count) const {
3261 virtual void DescribeTo(::std::ostream* os) const {
3262 *os << "called even number of times";
3266 Cardinality EvenNumber() {
3267 return MakeCardinality(new EvenNumberCardinality);
3271 EXPECT_CALL(foo, Bar(3))
3272 .Times(EvenNumber());
3275 ## Writing New Actions Quickly ##
3277 If the built-in actions don't work for you, and you find it
3278 inconvenient to use `Invoke()`, you can use a macro from the `ACTION*`
3279 family to quickly define a new action that can be used in your code as
3280 if it's a built-in action.
3284 ACTION(name) { statements; }
3286 in a namespace scope (i.e. not inside a class or function), you will
3287 define an action with the given name that executes the statements.
3288 The value returned by `statements` will be used as the return value of
3289 the action. Inside the statements, you can refer to the K-th
3290 (0-based) argument of the mock function as `argK`. For example:
3292 ACTION(IncrementArg1) { return ++(*arg1); }
3296 ... WillOnce(IncrementArg1());
3299 Note that you don't need to specify the types of the mock function
3300 arguments. Rest assured that your code is type-safe though:
3301 you'll get a compiler error if `*arg1` doesn't support the `++`
3302 operator, or if the type of `++(*arg1)` isn't compatible with the mock
3303 function's return type.
3314 defines an action `Foo()` that invokes argument #2 (a function pointer)
3315 with 5, calls function `Blah()`, sets the value pointed to by argument
3316 #1 to 0, and returns argument #0.
3318 For more convenience and flexibility, you can also use the following
3319 pre-defined symbols in the body of `ACTION`:
3321 | `argK_type` | The type of the K-th (0-based) argument of the mock function |
3322 |:------------|:-------------------------------------------------------------|
3323 | `args` | All arguments of the mock function as a tuple |
3324 | `args_type` | The type of all arguments of the mock function as a tuple |
3325 | `return_type` | The return type of the mock function |
3326 | `function_type` | The type of the mock function |
3328 For example, when using an `ACTION` as a stub action for mock function:
3330 int DoSomething(bool flag, int* ptr);
3334 | **Pre-defined Symbol** | **Is Bound To** |
3335 |:-----------------------|:----------------|
3336 | `arg0` | the value of `flag` |
3337 | `arg0_type` | the type `bool` |
3338 | `arg1` | the value of `ptr` |
3339 | `arg1_type` | the type `int*` |
3340 | `args` | the tuple `(flag, ptr)` |
3341 | `args_type` | the type `::testing::tuple<bool, int*>` |
3342 | `return_type` | the type `int` |
3343 | `function_type` | the type `int(bool, int*)` |
3345 ## Writing New Parameterized Actions Quickly ##
3347 Sometimes you'll want to parameterize an action you define. For that
3348 we have another macro
3350 ACTION_P(name, param) { statements; }
3355 ACTION_P(Add, n) { return arg0 + n; }
3357 will allow you to write
3359 // Returns argument #0 + 5.
3360 ... WillOnce(Add(5));
3363 For convenience, we use the term _arguments_ for the values used to
3364 invoke the mock function, and the term _parameters_ for the values
3365 used to instantiate an action.
3367 Note that you don't need to provide the type of the parameter either.
3368 Suppose the parameter is named `param`, you can also use the
3369 Google-Mock-defined symbol `param_type` to refer to the type of the
3370 parameter as inferred by the compiler. For example, in the body of
3371 `ACTION_P(Add, n)` above, you can write `n_type` for the type of `n`.
3373 Google Mock also provides `ACTION_P2`, `ACTION_P3`, and etc to support
3374 multi-parameter actions. For example,
3376 ACTION_P2(ReturnDistanceTo, x, y) {
3377 double dx = arg0 - x;
3378 double dy = arg1 - y;
3379 return sqrt(dx*dx + dy*dy);
3384 ... WillOnce(ReturnDistanceTo(5.0, 26.5));
3387 You can view `ACTION` as a degenerated parameterized action where the
3388 number of parameters is 0.
3390 You can also easily define actions overloaded on the number of parameters:
3392 ACTION_P(Plus, a) { ... }
3393 ACTION_P2(Plus, a, b) { ... }
3396 ## Restricting the Type of an Argument or Parameter in an ACTION ##
3398 For maximum brevity and reusability, the `ACTION*` macros don't ask
3399 you to provide the types of the mock function arguments and the action
3400 parameters. Instead, we let the compiler infer the types for us.
3402 Sometimes, however, we may want to be more explicit about the types.
3403 There are several tricks to do that. For example:
3406 // Makes sure arg0 can be converted to int.
3408 ... use n instead of arg0 here ...
3411 ACTION_P(Bar, param) {
3412 // Makes sure the type of arg1 is const char*.
3413 ::testing::StaticAssertTypeEq<const char*, arg1_type>();
3415 // Makes sure param can be converted to bool.
3419 where `StaticAssertTypeEq` is a compile-time assertion in Google Test
3420 that verifies two types are the same.
3422 ## Writing New Action Templates Quickly ##
3424 Sometimes you want to give an action explicit template parameters that
3425 cannot be inferred from its value parameters. `ACTION_TEMPLATE()`
3426 supports that and can be viewed as an extension to `ACTION()` and
3431 ACTION_TEMPLATE(ActionName,
3432 HAS_m_TEMPLATE_PARAMS(kind1, name1, ..., kind_m, name_m),
3433 AND_n_VALUE_PARAMS(p1, ..., p_n)) { statements; }
3436 defines an action template that takes _m_ explicit template parameters
3437 and _n_ value parameters, where _m_ is between 1 and 10, and _n_ is
3438 between 0 and 10. `name_i` is the name of the i-th template
3439 parameter, and `kind_i` specifies whether it's a `typename`, an
3440 integral constant, or a template. `p_i` is the name of the i-th value
3445 // DuplicateArg<k, T>(output) converts the k-th argument of the mock
3446 // function to type T and copies it to *output.
3447 ACTION_TEMPLATE(DuplicateArg,
3448 // Note the comma between int and k:
3449 HAS_2_TEMPLATE_PARAMS(int, k, typename, T),
3450 AND_1_VALUE_PARAMS(output)) {
3451 *output = T(::testing::get<k>(args));
3455 To create an instance of an action template, write:
3457 ActionName<t1, ..., t_m>(v1, ..., v_n)
3459 where the `t`s are the template arguments and the
3460 `v`s are the value arguments. The value argument
3461 types are inferred by the compiler. For example:
3466 EXPECT_CALL(mock, Foo(_, _))
3467 .WillOnce(DuplicateArg<1, unsigned char>(&n));
3470 If you want to explicitly specify the value argument types, you can
3471 provide additional template arguments:
3473 ActionName<t1, ..., t_m, u1, ..., u_k>(v1, ..., v_n)
3475 where `u_i` is the desired type of `v_i`.
3477 `ACTION_TEMPLATE` and `ACTION`/`ACTION_P*` can be overloaded on the
3478 number of value parameters, but not on the number of template
3479 parameters. Without the restriction, the meaning of the following is
3483 OverloadedAction<int, bool>(x);
3486 Are we using a single-template-parameter action where `bool` refers to
3487 the type of `x`, or a two-template-parameter action where the compiler
3488 is asked to infer the type of `x`?
3490 ## Using the ACTION Object's Type ##
3492 If you are writing a function that returns an `ACTION` object, you'll
3493 need to know its type. The type depends on the macro used to define
3494 the action and the parameter types. The rule is relatively simple:
3496 | **Given Definition** | **Expression** | **Has Type** |
3497 |:---------------------|:---------------|:-------------|
3498 | `ACTION(Foo)` | `Foo()` | `FooAction` |
3499 | `ACTION_TEMPLATE(Foo, HAS_m_TEMPLATE_PARAMS(...), AND_0_VALUE_PARAMS())` | `Foo<t1, ..., t_m>()` | `FooAction<t1, ..., t_m>` |
3500 | `ACTION_P(Bar, param)` | `Bar(int_value)` | `BarActionP<int>` |
3501 | `ACTION_TEMPLATE(Bar, HAS_m_TEMPLATE_PARAMS(...), AND_1_VALUE_PARAMS(p1))` | `Bar<t1, ..., t_m>(int_value)` | `FooActionP<t1, ..., t_m, int>` |
3502 | `ACTION_P2(Baz, p1, p2)` | `Baz(bool_value, int_value)` | `BazActionP2<bool, int>` |
3503 | `ACTION_TEMPLATE(Baz, HAS_m_TEMPLATE_PARAMS(...), AND_2_VALUE_PARAMS(p1, p2))`| `Baz<t1, ..., t_m>(bool_value, int_value)` | `FooActionP2<t1, ..., t_m, bool, int>` |
3506 Note that we have to pick different suffixes (`Action`, `ActionP`,
3507 `ActionP2`, and etc) for actions with different numbers of value
3508 parameters, or the action definitions cannot be overloaded on the
3511 ## Writing New Monomorphic Actions ##
3513 While the `ACTION*` macros are very convenient, sometimes they are
3514 inappropriate. For example, despite the tricks shown in the previous
3515 recipes, they don't let you directly specify the types of the mock
3516 function arguments and the action parameters, which in general leads
3517 to unoptimized compiler error messages that can baffle unfamiliar
3518 users. They also don't allow overloading actions based on parameter
3519 types without jumping through some hoops.
3521 An alternative to the `ACTION*` macros is to implement
3522 `::testing::ActionInterface<F>`, where `F` is the type of the mock
3523 function in which the action will be used. For example:
3526 template <typename F>class ActionInterface {
3528 virtual ~ActionInterface();
3530 // Performs the action. Result is the return type of function type
3531 // F, and ArgumentTuple is the tuple of arguments of F.
3533 // For example, if F is int(bool, const string&), then Result would
3534 // be int, and ArgumentTuple would be ::testing::tuple<bool, const string&>.
3535 virtual Result Perform(const ArgumentTuple& args) = 0;
3539 using ::testing::Action;
3540 using ::testing::ActionInterface;
3541 using ::testing::MakeAction;
3543 typedef int IncrementMethod(int*);
3545 class IncrementArgumentAction : public ActionInterface<IncrementMethod> {
3547 virtual int Perform(const ::testing::tuple<int*>& args) {
3548 int* p = ::testing::get<0>(args); // Grabs the first argument.
3553 Action<IncrementMethod> IncrementArgument() {
3554 return MakeAction(new IncrementArgumentAction);
3558 EXPECT_CALL(foo, Baz(_))
3559 .WillOnce(IncrementArgument());
3562 foo.Baz(&n); // Should return 5 and change n to 6.
3565 ## Writing New Polymorphic Actions ##
3567 The previous recipe showed you how to define your own action. This is
3568 all good, except that you need to know the type of the function in
3569 which the action will be used. Sometimes that can be a problem. For
3570 example, if you want to use the action in functions with _different_
3571 types (e.g. like `Return()` and `SetArgPointee()`).
3573 If an action can be used in several types of mock functions, we say
3574 it's _polymorphic_. The `MakePolymorphicAction()` function template
3575 makes it easy to define such an action:
3580 template <typename Impl>
3581 PolymorphicAction<Impl> MakePolymorphicAction(const Impl& impl);
3583 } // namespace testing
3586 As an example, let's define an action that returns the second argument
3587 in the mock function's argument list. The first step is to define an
3588 implementation class:
3591 class ReturnSecondArgumentAction {
3593 template <typename Result, typename ArgumentTuple>
3594 Result Perform(const ArgumentTuple& args) const {
3595 // To get the i-th (0-based) argument, use ::testing::get<i>(args).
3596 return ::testing::get<1>(args);
3601 This implementation class does _not_ need to inherit from any
3602 particular class. What matters is that it must have a `Perform()`
3603 method template. This method template takes the mock function's
3604 arguments as a tuple in a **single** argument, and returns the result of
3605 the action. It can be either `const` or not, but must be invokable
3606 with exactly one template argument, which is the result type. In other
3607 words, you must be able to call `Perform<R>(args)` where `R` is the
3608 mock function's return type and `args` is its arguments in a tuple.
3610 Next, we use `MakePolymorphicAction()` to turn an instance of the
3611 implementation class into the polymorphic action we need. It will be
3612 convenient to have a wrapper for this:
3615 using ::testing::MakePolymorphicAction;
3616 using ::testing::PolymorphicAction;
3618 PolymorphicAction<ReturnSecondArgumentAction> ReturnSecondArgument() {
3619 return MakePolymorphicAction(ReturnSecondArgumentAction());
3623 Now, you can use this polymorphic action the same way you use the
3629 class MockFoo : public Foo {
3631 MOCK_METHOD2(DoThis, int(bool flag, int n));
3632 MOCK_METHOD3(DoThat, string(int x, const char* str1, const char* str2));
3637 EXPECT_CALL(foo, DoThis(_, _))
3638 .WillOnce(ReturnSecondArgument());
3639 EXPECT_CALL(foo, DoThat(_, _, _))
3640 .WillOnce(ReturnSecondArgument());
3642 foo.DoThis(true, 5); // Will return 5.
3643 foo.DoThat(1, "Hi", "Bye"); // Will return "Hi".
3646 ## Teaching Google Mock How to Print Your Values ##
3648 When an uninteresting or unexpected call occurs, Google Mock prints the
3649 argument values and the stack trace to help you debug. Assertion
3650 macros like `EXPECT_THAT` and `EXPECT_EQ` also print the values in
3651 question when the assertion fails. Google Mock and Google Test do this using
3652 Google Test's user-extensible value printer.
3654 This printer knows how to print built-in C++ types, native arrays, STL
3655 containers, and any type that supports the `<<` operator. For other
3656 types, it prints the raw bytes in the value and hopes that you the
3657 user can figure it out.
3658 [Google Test's advanced guide](../../googletest/docs/advanced.md#teaching-google-test-how-to-print-your-values)
3659 explains how to extend the printer to do a better job at
3660 printing your particular type than to dump the bytes.