googlemock/docs/cheat

gMock Cheat Sheet

Defining a Mock Class

Mocking a Normal Class

Given

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

#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:

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.

Note: A mock object is currently naggy by default. We may make it nice by default in the future.

Mocking a Class Template

Class templates can be mocked just like any class.

To mock

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).

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,

  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

The typical work flow is:

Import the gMock names you need to use. All gMock symbols are in the testing namespace unless they are macros or otherwise noted.
Create the mock objects.
Optionally, set the default actions of the mock objects.
Set your expectations on the mock objects (How will they be called? What will they do?).
Exercise code that uses the mock objects; if necessary, check the result using googletest assertions.
When a mock object is destructed, gMock automatically verifies that all expectations on it have been satisfied.

Here's an example:

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("good", MyProductionFunction(&foo));  // #5
}                                                 // #6

Setting Default Actions

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:

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:

  // 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(nullptr, buzz1);
  EXPECT_NE(nullptr, buzz2);
  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 go/prefer-on-call for a more detailed discussion.

ON_CALL(mock-object, method(matchers))
    .With(multi-argument-matcher)   ?
    .WillByDefault(action);

Setting Expectations

EXPECT_CALL() sets expectations on a mock method (How will it be called? What will it do?):

EXPECT_CALL(mock-object, method (matchers)?)
     .With(multi-argument-matcher)  ?
     .Times(cardinality)            ?
     .InSequence(sequences)         *
     .After(expectations)           *
     .WillOnce(action)              *
     .WillRepeatedly(action)        ?
     .RetiresOnSaturation();        ?

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

A matcher matches a single argument. You can use it inside ON_CALL() or EXPECT_CALL(), or use it to validate a value directly:

Matcher	Description
`EXPECT_THAT(actual_value, matcher)`	Asserts that `actual_value` matches
: : `matcher`. :
`ASSERT_THAT(actual_value, matcher)`	The same as
: : `EXPECT_THAT(actual_value, matcher)`, :
: : except that it generates a fatal :
: : failure. :

Built-in matchers (where argument is the function argument) are divided into several categories:

Wildcard

Matcher	Description
`_`	`argument` can be any value of the correct type.
`A<type>()` or `An<type>()`	`argument` can be any value of type `type`.

Generic Comparison

Matcher	Description
`Eq(value)` or `value`	`argument == value`
`Ge(value)`	`argument >= value`
`Gt(value)`	`argument > value`
`Le(value)`	`argument <= value`
`Lt(value)`	`argument < value`
`Ne(value)`	`argument != value`
`IsNull()`	`argument` is a `NULL` pointer (raw or smart).
`NotNull()`	`argument` is a non-null pointer (raw or smart).
`Optional(m)`	`argument` is `optional<>` that contains a value
: : matching `m`. :
`VariantWith<T>(m)`	`argument` is `variant<>` that holds the
: : alternative of type T with a value matching `m`. :
`Ref(variable)`	`argument` is a reference to `variable`.
`TypedEq<type>(value)`	`argument` has type `type` and is equal to `value`.
: : You may need to use this instead of `Eq(value)` :
: : when the mock function is overloaded. :

Except Ref(), these matchers make a copy of value in case it‘s modified or destructed later. If the compiler complains that value doesn’t have a public copy constructor, try wrap it in ByRef(), e.g. Eq(ByRef(non_copyable_value)). If you do that, make sure non_copyable_value is not changed afterwards, or the meaning of your matcher will be changed.

Floating-Point Matchers

Matcher	Description
`DoubleEq(a_double)`	`argument` is a `double` value
: : approximately equal to `a_double`, :
: : treating two NaNs as unequal. :
`FloatEq(a_float)`	`argument` is a `float` value
: : approximately equal to `a_float`, :
: : treating two NaNs as unequal. :
`NanSensitiveDoubleEq(a_double)`	`argument` is a `double` value
: : approximately equal to `a_double`, :
: : treating two NaNs as equal. :
`NanSensitiveFloatEq(a_float)`	`argument` is a `float` value
: : approximately equal to `a_float`, :
: : treating two NaNs as equal. :

The above matchers use ULP-based comparison (the same as used in googletest). They automatically pick a reasonable error bound based on the absolute value of the expected value. DoubleEq() and FloatEq() conform to the IEEE standard, which requires comparing two NaNs for equality to return false. The NanSensitive* version instead treats two NaNs as equal, which is often what a user wants.

Matcher	Description
`DoubleNear(a_double,	`argument` is a `double` value close
: max_abs_error) `: to`a_double` (absolute error <= :
: : `max_abs_error`), treating two NaNs as :
: : unequal. :
`FloatNear(a_float, max_abs_error)`	`argument` is a `float` value close to
: : `a_float` (absolute error <= :
: : `max_abs_error`), treating two NaNs as :
: : unequal. :
`NanSensitiveDoubleNear(a_double,	`argument` is a `double` value close
: max_abs_error) `: to`a_double` (absolute error <= :
: : `max_abs_error`), treating two NaNs as :
: : equal. :
`NanSensitiveFloatNear(a_float,	`argument` is a `float` value close to
: max_abs_error) `:`a_float` (absolute error <= :
: : `max_abs_error`), treating two NaNs as :
: : equal. :

String Matchers

The argument can be either a C string or a C++ string object:

Matcher	Description
`ContainsRegex(string)`	`argument` matches the given regular expression.
`EndsWith(suffix)`	`argument` ends with string `suffix`.
`HasSubstr(string)`	`argument` contains `string` as a sub-string.
`MatchesRegex(string)`	`argument` matches the given regular expression
: : with the match starting at the first character and :
: : ending at the last character. :
`StartsWith(prefix)`	`argument` starts with string `prefix`.
`StrCaseEq(string)`	`argument` is equal to `string`, ignoring case.
`StrCaseNe(string)`	`argument` is not equal to `string`, ignoring
: : case. :
`StrEq(string)`	`argument` is equal to `string`.
`StrNe(string)`	`argument` is not equal to `string`.

ContainsRegex() and MatchesRegex() take ownership of the RE object. They use the regular expression syntax defined here. StrCaseEq(), StrCaseNe(), StrEq(), and StrNe() work for wide strings as well.

Container Matchers

Most STL-style containers support ==, so you can use Eq(expected_container) or simply expected_container to match a container exactly. If you want to write the elements in-line, match them more flexibly, or get more informative messages, you can use:

Matcher	Description
`ContainerEq(container)`	The same as `Eq(container)` except
: : that the failure message also :
: : includes which elements are in one :
: : container but not the other. :
`Contains(e)`	`argument` contains an element that
: : matches `e`, which can be either a :
: : value or a matcher. :
`Each(e)`	`argument` is a container where
: : every element matches `e`, which :
: : can be either a value or a matcher. :
`ElementsAre(e0, e1, ..., en)`	`argument` has `n + 1` elements,
: : where the i-th element matches `ei`, :
: : which can be a value or a matcher. 0 :
: : to 10 arguments are allowed. :
`ElementsAreArray({ e0, e1, ..., en	The same as `ElementsAre()` except
: })`,` ElementsAreArray(array)`, or : that the expected element :
: `ElementsAreArray(array, count)` : values/matchers come from an :
: : initializer list, STL-style :
: : container, or C-style array. :
`IsEmpty()`	`argument` is an empty container
: : (`container.empty()`). :
`Pointwise(m, container)`	`argument` contains the same number
: : of elements as in `container`, and :
: : for all i, (the i-th element in :
: : `argument`, the i-th element in :
: : `container`) match `m`, which is a :
: : matcher on 2-tuples. E.g. :
: : `Pointwise(Le(), upper_bounds)` :
: : verifies that each element in :
: : `argument` doesn't exceed the :
: : corresponding element in :
: : `upper_bounds`. See more detail :
: : below. :
`SizeIs(m)`	`argument` is a container whose size
: : matches `m`. E.g. `SizeIs(2)` or :
: : `SizeIs(Lt(2))`. :
`UnorderedElementsAre(e0, e1, ...,	`argument` has `n + 1` elements, and
: en)` : under some permutation each element :
: : matches an `ei` (for a different :
: : `i`), which can be a value or a :
: : matcher. 0 to 10 arguments are :
: : allowed. :
`UnorderedElementsAreArray({ e0, e1,	The same as `UnorderedElementsAre()`
: ..., en })`, : except that the expected element :
: `UnorderedElementsAreArray(array)`, : values/matchers come from an :
: or `UnorderedElementsAreArray(array, : initializer list, STL-style :
: count)` : container, or C-style array. :
`WhenSorted(m)`	When `argument` is sorted using the
: : `<` operator, it matches container :
: : matcher `m`. E.g. :
: : `WhenSorted(ElementsAre(1, 2, 3))` :
: : verifies that `argument` contains :
: : elements `1`, `2`, and `3`, ignoring :
: : order. :
`WhenSortedBy(comparator, m)`	The same as `WhenSorted(m)`, except
: : that the given comparator instead of :
: : `<` is used to sort `argument`. E.g. :
: : `WhenSortedBy(std::greater(), :
: : ElementsAre(3, 2, 1))`. :

Notes:

These matchers can also match:
1. a native array passed by reference (e.g. in Foo(const int (&a)[5])), and
2. an array passed as a pointer and a count (e.g. in Bar(const T* buffer, int len) -- see Multi-argument Matchers).
The array being matched may be multi-dimensional (i.e. its elements can be arrays).
m in Pointwise(m, ...) should be a matcher for ::std::tuple<T, U> where T and U are the element type of the actual container and the expected container, respectively. For example, to compare two Foo containers where Foo doesn't support operator==, one might write:
```
using ::std::get;
MATCHER(FooEq, "") {
  return std::get<0>(arg).Equals(std::get<1>(arg));
}
...
EXPECT_THAT(actual_foos, Pointwise(FooEq(), expected_foos));
```

Member Matchers

Matcher	Description
`Field(&class::field, m)`	`argument.field` (or `argument->field`
: : when `argument` is a plain pointer) :
: : matches matcher `m`, where `argument` is :
: : an object of type class. :
`Key(e)`	`argument.first` matches `e`, which can be
: : either a value or a matcher. E.g. :
: : `Contains(Key(Le(5)))` can verify that a :
: : `map` contains a key `<= 5`. :
`Pair(m1, m2)`	`argument` is an `std::pair` whose `first`
: : field matches `m1` and `second` field :
: : matches `m2`. :
`Property(&class::property, m)`	`argument.property()` (or
: : `argument->property()` when `argument` is :
: : a plain pointer) matches matcher `m`, :
: : where `argument` is an object of type :
: : class. :

Matching the Result of a Function, Functor, or Callback

Matcher	Description
`ResultOf(f, m)`	`f(argument)` matches matcher `m`, where `f` is a
: : function or functor. :

Pointer Matchers

Matcher	Description
`Pointee(m)`	`argument` (either a smart pointer or a raw
: : pointer) points to a value that matches matcher :
: : `m`. :
`WhenDynamicCastTo<T>(m)`	when `argument` is passed through
: : `dynamic_cast<T>()`, it matches matcher `m`. :

Multi-argument Matchers

Technically, all matchers match a single value. A “multi-argument” matcher is just one that matches a tuple. The following matchers can be used to match a tuple (x, y):

Matcher	Description
`Eq()`	`x == y`
`Ge()`	`x >= y`
`Gt()`	`x > y`
`Le()`	`x <= y`
`Lt()`	`x < y`
`Ne()`	`x != y`

You can use the following selectors to pick a subset of the arguments (or reorder them) to participate in the matching:

Matcher	Description
`AllArgs(m)`	Equivalent to `m`. Useful as syntactic sugar in
: : `.With(AllArgs(m))`. :
`Args<N1, N2, ..., Nk>(m)`	The tuple of the `k` selected (using 0-based
: : indices) arguments matches `m`, e.g. `Args<1, :
: : 2>(Eq())`. :

Composite Matchers

You can make a matcher from one or more other matchers:

Matcher	Description
`AllOf(m1, m2, ..., mn)`	`argument` matches all of the matchers `m1` to
: : `mn`. :
`AnyOf(m1, m2, ..., mn)`	`argument` matches at least one of the matchers
: : `m1` to `mn`. :
`Not(m)`	`argument` doesn't match matcher `m`.

Adapters for Matchers

Matcher	Description
`MatcherCast<T>(m)`	casts matcher `m` to type
: : `Matcher<T>`. :
`SafeMatcherCast<T>(m)`	[safely
: : casts](cook_book.md#casting-matchers) :
: : matcher `m` to type `Matcher<T>`. :
`Truly(predicate)`	`predicate(argument)` returns
: : something considered by C++ to be :
: : true, where `predicate` is a function :
: : or functor. :

AddressSatisfies(callback) and Truly(callback) take ownership of callback, which must be a permanent callback.

Matchers as Predicates

Matcher	Description
`Matches(m)(value)`	evaluates to `true` if `value` matches `m`.
: : You can use `Matches(m)` alone as a unary :
: : functor. :
`ExplainMatchResult(m, value,	evaluates to `true` if `value` matches `m`,
: result_listener) `: explaining the result to`result_listener`. :
`Value(value, m)`	evaluates to `true` if `value` matches `m`.

Defining Matchers

Matcher	Description
`MATCHER(IsEven, "") { return (arg %	Defines a matcher `IsEven()` to match
: 2) == 0; }` : an even number. :
`MATCHER_P(IsDivisibleBy, n, "") {	Defines a macher `IsDivisibleBy(n)`
: *result_listener << "where the : to match a number divisible by `n`. :
: remainder is " << (arg % n); return : :
: (arg % n) == 0; }` : :
`MATCHER_P2(IsBetween, a, b,	Defines a matcher `IsBetween(a, b)`
: std::string(negation ? “isn't” : : to match a value in the range [`a`, :
: “is”) + " between " + : `b`]. :
: PrintToString(a) + " and " + : :
: PrintToString(b)) { return a <= arg : :
: && arg <= b; }` : :

Notes:

The MATCHER* macros cannot be used inside a function or class.
The matcher body 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).
You can use PrintToString(x) to convert a value x of any type to a string.

Matchers as Test Assertions

Matcher	Description
`ASSERT_THAT(expression, m)`	Generates a fatal failure if the value of `expression` doesn't match matcher `m`.
`EXPECT_THAT(expression, m)`	Generates a non-fatal failure if the value of `expression` doesn't match matcher `m`.

Actions

Actions specify what a mock function should do when invoked.

Returning a Value

Matcher	Description
`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 at :
: : the time the expectation is set, 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. :

Side Effects

Matcher	Description
`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, Lambda, or Callback as an Action

In the following, by “callable” we mean a free function, std::function, functor, lambda, or google3-style permanent callback.

Matcher	Description
`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,	Invoke the {method on the object with
: &class::method)` : 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,	Invoke the method on the object, which
: &class::method)` : takes no arguments. :
`InvokeArgument(arg1, arg2, ...,	Invoke the mock function's `N`-th
: argk)` : (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:

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.

  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 ByRef(). For example,

using ::testing::ByRef;
using ::testing::InvokeArgument;
...
InvokeArgument<2>(5, string("Hi"), ByRef(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). :

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

Matcher	Description
`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. :
`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

Matcher	Description
`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 +	Defines an action `Plus(n)` to return
: n; }` : the sum of the mock function's :
: : argument #0 and `n`. :
`ACTION_Pk(Foo, p1, ..., pk) {	Defines a parameterized action `Foo(p1,
: statements; } `: ..., pk)` to execute the given :
: : `statements`. :

The ACTION* macros cannot be used inside a function or class.

Cardinalities

These are used in Times() to specify how many times a mock function will be called:

Matcher	Description
`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

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:

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

When you have a long chain of sequential expectations, it‘s easier to specify the order using sequences, which don’t require you to given each expectation in the chain a different name. All expected calls in the same sequence must occur in the order they are specified.

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:

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:

using ::testing::Mock;
...
// Verifies and removes the expectations on mock_obj;
// returns true iff successful.
Mock::VerifyAndClearExpectations(&mock_obj);
...
// Verifies and removes the expectations on mock_obj;
// also removes the default actions set by ON_CALL();
// returns true iff successful.
Mock::VerifyAndClear(&mock_obj);

You can also tell gMock that a mock object can be leaked and doesn't need to be verified:

Mock::AllowLeak(&mock_obj);

Mock Classes

gMock defines a convenient mock class template

class MockFunction<R(A1, ..., An)> {
 public:
  MOCK_METHOD(R, Call, (A1, ..., An));
};

See this recipe 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. :