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diff --git a/docs/gmock_cheat_sheet.md b/docs/gmock_cheat_sheet.md new file mode 100644 index 00000000..cda9ddd5 --- /dev/null +++ b/docs/gmock_cheat_sheet.md @@ -0,0 +1,483 @@ +# gMock Cheat Sheet + +## Defining a Mock Class + +### Mocking a Normal Class {#MockClass} + +Given + +```cpp +class Foo { + ... + virtual ~Foo(); + virtual int GetSize() const = 0; + virtual string Describe(const char* name) = 0; + virtual string Describe(int type) = 0; + virtual bool Process(Bar elem, int count) = 0; +}; +``` + +(note that `~Foo()` **must** be virtual) we can define its mock as + +```cpp +#include "gmock/gmock.h" + +class MockFoo : public Foo { + ... + MOCK_METHOD(int, GetSize, (), (const, override)); + MOCK_METHOD(string, Describe, (const char* name), (override)); + MOCK_METHOD(string, Describe, (int type), (override)); + MOCK_METHOD(bool, Process, (Bar elem, int count), (override)); +}; +``` + +To create a "nice" mock, which ignores all uninteresting calls, a "naggy" mock, +which warns on all uninteresting calls, or a "strict" mock, which treats them as +failures: + +```cpp +using ::testing::NiceMock; +using ::testing::NaggyMock; +using ::testing::StrictMock; + +NiceMock<MockFoo> nice_foo; // The type is a subclass of MockFoo. +NaggyMock<MockFoo> naggy_foo; // The type is a subclass of MockFoo. +StrictMock<MockFoo> strict_foo; // The type is a subclass of MockFoo. +``` + +{: .callout .note} +**Note:** A mock object is currently naggy by default. We may make it nice by +default in the future. + +### Mocking a Class Template {#MockTemplate} + +Class templates can be mocked just like any class. + +To mock + +```cpp +template <typename Elem> +class StackInterface { + ... + virtual ~StackInterface(); + virtual int GetSize() const = 0; + virtual void Push(const Elem& x) = 0; +}; +``` + +(note that all member functions that are mocked, including `~StackInterface()` +**must** be virtual). + +```cpp +template <typename Elem> +class MockStack : public StackInterface<Elem> { + ... + MOCK_METHOD(int, GetSize, (), (const, override)); + MOCK_METHOD(void, Push, (const Elem& x), (override)); +}; +``` + +### Specifying Calling Conventions for Mock Functions + +If your mock function doesn't use the default calling convention, you can +specify it by adding `Calltype(convention)` to `MOCK_METHOD`'s 4th parameter. +For example, + +```cpp + MOCK_METHOD(bool, Foo, (int n), (Calltype(STDMETHODCALLTYPE))); + MOCK_METHOD(int, Bar, (double x, double y), + (const, Calltype(STDMETHODCALLTYPE))); +``` + +where `STDMETHODCALLTYPE` is defined by `<objbase.h>` on Windows. + +## Using Mocks in Tests {#UsingMocks} + +The typical work flow is: + +1. Import the gMock names you need to use. All gMock symbols are in the + `testing` namespace unless they are macros or otherwise noted. +2. Create the mock objects. +3. Optionally, set the default actions of the mock objects. +4. Set your expectations on the mock objects (How will they be called? What + will they do?). +5. Exercise code that uses the mock objects; if necessary, check the result + using googletest assertions. +6. When a mock object is destructed, gMock automatically verifies that all + expectations on it have been satisfied. + +Here's an example: + +```cpp +using ::testing::Return; // #1 + +TEST(BarTest, DoesThis) { + MockFoo foo; // #2 + + ON_CALL(foo, GetSize()) // #3 + .WillByDefault(Return(1)); + // ... other default actions ... + + EXPECT_CALL(foo, Describe(5)) // #4 + .Times(3) + .WillRepeatedly(Return("Category 5")); + // ... other expectations ... + + EXPECT_EQ(MyProductionFunction(&foo), "good"); // #5 +} // #6 +``` + +## Setting Default Actions {#OnCall} + +gMock has a **built-in default action** for any function that returns `void`, +`bool`, a numeric value, or a pointer. In C++11, it will additionally returns +the default-constructed value, if one exists for the given type. + +To customize the default action for functions with return type *`T`*: + +```cpp +using ::testing::DefaultValue; + +// Sets the default value to be returned. T must be CopyConstructible. +DefaultValue<T>::Set(value); +// Sets a factory. Will be invoked on demand. T must be MoveConstructible. +// T MakeT(); +DefaultValue<T>::SetFactory(&MakeT); +// ... use the mocks ... +// Resets the default value. +DefaultValue<T>::Clear(); +``` + +Example usage: + +```cpp + // Sets the default action for return type std::unique_ptr<Buzz> to + // creating a new Buzz every time. + DefaultValue<std::unique_ptr<Buzz>>::SetFactory( + [] { return MakeUnique<Buzz>(AccessLevel::kInternal); }); + + // When this fires, the default action of MakeBuzz() will run, which + // will return a new Buzz object. + EXPECT_CALL(mock_buzzer_, MakeBuzz("hello")).Times(AnyNumber()); + + auto buzz1 = mock_buzzer_.MakeBuzz("hello"); + auto buzz2 = mock_buzzer_.MakeBuzz("hello"); + EXPECT_NE(buzz1, nullptr); + EXPECT_NE(buzz2, nullptr); + EXPECT_NE(buzz1, buzz2); + + // Resets the default action for return type std::unique_ptr<Buzz>, + // to avoid interfere with other tests. + DefaultValue<std::unique_ptr<Buzz>>::Clear(); +``` + +To customize the default action for a particular method of a specific mock +object, use `ON_CALL()`. `ON_CALL()` has a similar syntax to `EXPECT_CALL()`, +but it is used for setting default behaviors (when you do not require that the +mock method is called). See [here](gmock_cook_book.md#UseOnCall) for a more +detailed discussion. + +```cpp +ON_CALL(mock-object, method(matchers)) + .With(multi-argument-matcher) ? + .WillByDefault(action); +``` + +## Setting Expectations {#ExpectCall} + +`EXPECT_CALL()` sets **expectations** on a mock method (How will it be called? +What will it do?): + +```cpp +EXPECT_CALL(mock-object, method (matchers)?) + .With(multi-argument-matcher) ? + .Times(cardinality) ? + .InSequence(sequences) * + .After(expectations) * + .WillOnce(action) * + .WillRepeatedly(action) ? + .RetiresOnSaturation(); ? +``` + +For each item above, `?` means it can be used at most once, while `*` means it +can be used any number of times. + +In order to pass, `EXPECT_CALL` must be used before the calls are actually made. + +The `(matchers)` is a comma-separated list of matchers that correspond to each +of the arguments of `method`, and sets the expectation only for calls of +`method` that matches all of the matchers. + +If `(matchers)` is omitted, the expectation is the same as if the matchers were +set to anything matchers (for example, `(_, _, _, _)` for a four-arg method). + +If `Times()` is omitted, the cardinality is assumed to be: + +* `Times(1)` when there is neither `WillOnce()` nor `WillRepeatedly()`; +* `Times(n)` when there are `n` `WillOnce()`s but no `WillRepeatedly()`, where + `n` >= 1; or +* `Times(AtLeast(n))` when there are `n` `WillOnce()`s and a + `WillRepeatedly()`, where `n` >= 0. + +A method with no `EXPECT_CALL()` is free to be invoked *any number of times*, +and the default action will be taken each time. + +## Matchers {#MatcherList} + +See the [Matchers Reference](reference/matchers.md). + +## Actions {#ActionList} + +**Actions** specify what a mock function should do when invoked. + +### Returning a Value + +| | | +| :-------------------------------- | :-------------------------------------------- | +| `Return()` | Return from a `void` mock function. | +| `Return(value)` | Return `value`. If the type of `value` is different to the mock function's return type, `value` is converted to the latter type <i>at the time the expectation is set</i>, not when the action is executed. | +| `ReturnArg<N>()` | Return the `N`-th (0-based) argument. | +| `ReturnNew<T>(a1, ..., ak)` | Return `new T(a1, ..., ak)`; a different object is created each time. | +| `ReturnNull()` | Return a null pointer. | +| `ReturnPointee(ptr)` | Return the value pointed to by `ptr`. | +| `ReturnRef(variable)` | Return a reference to `variable`. | +| `ReturnRefOfCopy(value)` | Return a reference to a copy of `value`; the copy lives as long as the action. | +| `ReturnRoundRobin({a1, ..., ak})` | Each call will return the next `ai` in the list, starting at the beginning when the end of the list is reached. | + +### Side Effects + +| | | +| :--------------------------------- | :-------------------------------------- | +| `Assign(&variable, value)` | Assign `value` to variable. | +| `DeleteArg<N>()` | Delete the `N`-th (0-based) argument, which must be a pointer. | +| `SaveArg<N>(pointer)` | Save the `N`-th (0-based) argument to `*pointer`. | +| `SaveArgPointee<N>(pointer)` | Save the value pointed to by the `N`-th (0-based) argument to `*pointer`. | +| `SetArgReferee<N>(value)` | Assign `value` to the variable referenced by the `N`-th (0-based) argument. | +| `SetArgPointee<N>(value)` | Assign `value` to the variable pointed by the `N`-th (0-based) argument. | +| `SetArgumentPointee<N>(value)` | Same as `SetArgPointee<N>(value)`. Deprecated. Will be removed in v1.7.0. | +| `SetArrayArgument<N>(first, last)` | Copies the elements in source range [`first`, `last`) to the array pointed to by the `N`-th (0-based) argument, which can be either a pointer or an iterator. The action does not take ownership of the elements in the source range. | +| `SetErrnoAndReturn(error, value)` | Set `errno` to `error` and return `value`. | +| `Throw(exception)` | Throws the given exception, which can be any copyable value. Available since v1.1.0. | + +### Using a Function, Functor, or Lambda as an Action + +In the following, by "callable" we mean a free function, `std::function`, +functor, or lambda. + +| | | +| :---------------------------------- | :------------------------------------- | +| `f` | Invoke f with the arguments passed to the mock function, where f is a callable. | +| `Invoke(f)` | Invoke `f` with the arguments passed to the mock function, where `f` can be a global/static function or a functor. | +| `Invoke(object_pointer, &class::method)` | Invoke the method on the object with the arguments passed to the mock function. | +| `InvokeWithoutArgs(f)` | Invoke `f`, which can be a global/static function or a functor. `f` must take no arguments. | +| `InvokeWithoutArgs(object_pointer, &class::method)` | Invoke the method on the object, which takes no arguments. | +| `InvokeArgument<N>(arg1, arg2, ..., argk)` | Invoke the mock function's `N`-th (0-based) argument, which must be a function or a functor, with the `k` arguments. | + +The return value of the invoked function is used as the return value of the +action. + +When defining a callable to be used with `Invoke*()`, you can declare any unused +parameters as `Unused`: + +```cpp +using ::testing::Invoke; +double Distance(Unused, double x, double y) { return sqrt(x*x + y*y); } +... +EXPECT_CALL(mock, Foo("Hi", _, _)).WillOnce(Invoke(Distance)); +``` + +`Invoke(callback)` and `InvokeWithoutArgs(callback)` take ownership of +`callback`, which must be permanent. The type of `callback` must be a base +callback type instead of a derived one, e.g. + +```cpp + BlockingClosure* done = new BlockingClosure; + ... Invoke(done) ...; // This won't compile! + + Closure* done2 = new BlockingClosure; + ... Invoke(done2) ...; // This works. +``` + +In `InvokeArgument<N>(...)`, if an argument needs to be passed by reference, +wrap it inside `std::ref()`. For example, + +```cpp +using ::testing::InvokeArgument; +... +InvokeArgument<2>(5, string("Hi"), std::ref(foo)) +``` + +calls the mock function's #2 argument, passing to it `5` and `string("Hi")` by +value, and `foo` by reference. + +### Default Action + +| Matcher | Description | +| :------------ | :----------------------------------------------------- | +| `DoDefault()` | Do the default action (specified by `ON_CALL()` or the built-in one). | + +{: .callout .note} +**Note:** due to technical reasons, `DoDefault()` cannot be used inside a +composite action - trying to do so will result in a run-time error. + +### Composite Actions + +| | | +| :----------------------------- | :------------------------------------------ | +| `DoAll(a1, a2, ..., an)` | Do all actions `a1` to `an` and return the result of `an` in each invocation. The first `n - 1` sub-actions must return void and will receive a readonly view of the arguments. | +| `IgnoreResult(a)` | Perform action `a` and ignore its result. `a` must not return void. | +| `WithArg<N>(a)` | Pass the `N`-th (0-based) argument of the mock function to action `a` and perform it. | +| `WithArgs<N1, N2, ..., Nk>(a)` | Pass the selected (0-based) arguments of the mock function to action `a` and perform it. | +| `WithoutArgs(a)` | Perform action `a` without any arguments. | + +### Defining Actions + +| | | +| :--------------------------------- | :-------------------------------------- | +| `ACTION(Sum) { return arg0 + arg1; }` | Defines an action `Sum()` to return the sum of the mock function's argument #0 and #1. | +| `ACTION_P(Plus, n) { return arg0 + n; }` | Defines an action `Plus(n)` to return the sum of the mock function's argument #0 and `n`. | +| `ACTION_Pk(Foo, p1, ..., pk) { statements; }` | Defines a parameterized action `Foo(p1, ..., pk)` to execute the given `statements`. | + +The `ACTION*` macros cannot be used inside a function or class. + +## Cardinalities {#CardinalityList} + +These are used in `Times()` to specify how many times a mock function will be +called: + +| | | +| :---------------- | :----------------------------------------------------- | +| `AnyNumber()` | The function can be called any number of times. | +| `AtLeast(n)` | The call is expected at least `n` times. | +| `AtMost(n)` | The call is expected at most `n` times. | +| `Between(m, n)` | The call is expected between `m` and `n` (inclusive) times. | +| `Exactly(n) or n` | The call is expected exactly `n` times. In particular, the call should never happen when `n` is 0. | + +## Expectation Order + +By default, the expectations can be matched in *any* order. If some or all +expectations must be matched in a given order, there are two ways to specify it. +They can be used either independently or together. + +### The After Clause {#AfterClause} + +```cpp +using ::testing::Expectation; +... +Expectation init_x = EXPECT_CALL(foo, InitX()); +Expectation init_y = EXPECT_CALL(foo, InitY()); +EXPECT_CALL(foo, Bar()) + .After(init_x, init_y); +``` + +says that `Bar()` can be called only after both `InitX()` and `InitY()` have +been called. + +If you don't know how many pre-requisites an expectation has when you write it, +you can use an `ExpectationSet` to collect them: + +```cpp +using ::testing::ExpectationSet; +... +ExpectationSet all_inits; +for (int i = 0; i < element_count; i++) { + all_inits += EXPECT_CALL(foo, InitElement(i)); +} +EXPECT_CALL(foo, Bar()) + .After(all_inits); +``` + +says that `Bar()` can be called only after all elements have been initialized +(but we don't care about which elements get initialized before the others). + +Modifying an `ExpectationSet` after using it in an `.After()` doesn't affect the +meaning of the `.After()`. + +### Sequences {#UsingSequences} + +When you have a long chain of sequential expectations, it's easier to specify +the order using **sequences**, which don't require you to give each expectation +in the chain a different name. *All expected calls* in the same sequence must +occur in the order they are specified. + +```cpp +using ::testing::Return; +using ::testing::Sequence; +Sequence s1, s2; +... +EXPECT_CALL(foo, Reset()) + .InSequence(s1, s2) + .WillOnce(Return(true)); +EXPECT_CALL(foo, GetSize()) + .InSequence(s1) + .WillOnce(Return(1)); +EXPECT_CALL(foo, Describe(A<const char*>())) + .InSequence(s2) + .WillOnce(Return("dummy")); +``` + +says that `Reset()` must be called before *both* `GetSize()` *and* `Describe()`, +and the latter two can occur in any order. + +To put many expectations in a sequence conveniently: + +```cpp +using ::testing::InSequence; +{ + InSequence seq; + + EXPECT_CALL(...)...; + EXPECT_CALL(...)...; + ... + EXPECT_CALL(...)...; +} +``` + +says that all expected calls in the scope of `seq` must occur in strict order. +The name `seq` is irrelevant. + +## Verifying and Resetting a Mock + +gMock will verify the expectations on a mock object when it is destructed, or +you can do it earlier: + +```cpp +using ::testing::Mock; +... +// Verifies and removes the expectations on mock_obj; +// returns true if and only if successful. +Mock::VerifyAndClearExpectations(&mock_obj); +... +// Verifies and removes the expectations on mock_obj; +// also removes the default actions set by ON_CALL(); +// returns true if and only if successful. +Mock::VerifyAndClear(&mock_obj); +``` + +You can also tell gMock that a mock object can be leaked and doesn't need to be +verified: + +```cpp +Mock::AllowLeak(&mock_obj); +``` + +## Mock Classes + +gMock defines a convenient mock class template + +```cpp +class MockFunction<R(A1, ..., An)> { + public: + MOCK_METHOD(R, Call, (A1, ..., An)); +}; +``` + +See this [recipe](gmock_cook_book.md#using-check-points) for one application of +it. + +## Flags + +| Flag | Description | +| :----------------------------- | :---------------------------------------- | +| `--gmock_catch_leaked_mocks=0` | Don't report leaked mock objects as failures. | +| `--gmock_verbose=LEVEL` | Sets the default verbosity level (`info`, `warning`, or `error`) of Google Mock messages. | |