# 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_CONST_METHOD0(GetSize, int());
  MOCK_METHOD1(Describe, string(const char* name));
  MOCK_METHOD1(Describe, string(int type));
  MOCK_METHOD2(Process, bool(Bar elem, int count));
};
```

To create a "nice" mock object which ignores all uninteresting calls,
or a "strict" mock object, which treats them as failures:
```
NiceMock<MockFoo> nice_foo;     // The type is a subclass of MockFoo.
StrictMock<MockFoo> strict_foo; // The type is a subclass of MockFoo.
```

## Mocking a Class Template ##

To mock
```
template <typename Elem>
class StackInterface {
 public:
  ...
  virtual ~StackInterface();
  virtual int GetSize() const = 0;
  virtual void Push(const Elem& x) = 0;
};
```
(note that `~StackInterface()` **must** be virtual) just append `_T` to the `MOCK_*` macros:
```
template <typename Elem>
class MockStack : public StackInterface<Elem> {
 public:
  ...
  MOCK_CONST_METHOD0_T(GetSize, int());
  MOCK_METHOD1_T(Push, void(const Elem& x));
};
```

## Specifying Calling Conventions for Mock Functions ##

If your mock function doesn't use the default calling convention, you
can specify it by appending `_WITH_CALLTYPE` to any of the macros
described in the previous two sections and supplying the calling
convention as the first argument to the macro. For example,
```
  MOCK_METHOD_1_WITH_CALLTYPE(STDMETHODCALLTYPE, Foo, bool(int n));
  MOCK_CONST_METHOD2_WITH_CALLTYPE(STDMETHODCALLTYPE, Bar, int(double x, double y));
```
where `STDMETHODCALLTYPE` is defined by `<objbase.h>` on Windows.

# Using Mocks in Tests #

The typical flow is:
  1. Import the Google Mock names you need to use. All Google Mock names are in the `testing` namespace unless they are macros or otherwise noted.
  1. Create the mock objects.
  1. Optionally, set the default actions of the mock objects.
  1. Set your expectations on the mock objects (How will they be called? What wil they do?).
  1. Exercise code that uses the mock objects; if necessary, check the result using [Google Test](http://code.google.com/p/googletest/) assertions.
  1. When a mock objects is destructed, Google Mock automatically verifies that all expectations on it have been satisfied.

Here is 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 #

Google Mock has a **built-in default action** for any function that
returns `void`, `bool`, a numeric value, or a pointer.

To customize the default action for functions with return type `T` globally:
```
using ::testing::DefaultValue;

DefaultValue<T>::Set(value);  // Sets the default value to be returned.
// ... use the mocks ...
DefaultValue<T>::Clear();     // Resets the default value.
```

To customize the default action for a particular method, use `ON_CALL()`:
```
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 `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:

| `EXPECT_THAT(value, matcher)` | Asserts that `value` matches `matcher`. |
|:------------------------------|:----------------------------------------|
| `ASSERT_THAT(value, matcher)` | The same as `EXPECT_THAT(value, matcher)`, except that it generates a **fatal** failure. |

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

## Wildcard ##
|`_`|`argument` can be any value of the correct type.|
|:--|:-----------------------------------------------|
|`A<type>()` or `An<type>()`|`argument` can be any value of type `type`.     |

## Generic Comparison ##

|`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).|
|`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 ##

|`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
[Google Test](http://code.google.com/p/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.

## String Matchers ##

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

|`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`.            |

`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:

| `Contains(e)` | `argument` contains an element that 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(array)` or `ElementsAreArray(array, count)`|The same as `ElementsAre()` except that the expected element values/matchers come from a C-style array.|
| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. |

These matchers can also match:

  1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`), and
  1. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer, int len)` -- see [Multi-argument Matchers](#Multiargument_Matchers.md)).

where the array may be multi-dimensional (i.e. its elements can be arrays).

## Member Matchers ##

|`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 or Functor ##

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

## Pointer Matchers ##

|`Pointee(m)`|`argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`.|
|:-----------|:-----------------------------------------------------------------------------------------------|

## Multiargument Matchers ##

These are matchers on tuple types. They can be used in
`.With()`. The following can be used on functions with <i>two<br>
arguments</i> `x` and `y`:

|`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:

|`AllArgs(m)`|Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`.|
|:-----------|:-------------------------------------------------------------------|
|`Args<N1, N2, ..., Nk>(m)`|The `k` selected (using 0-based indices) arguments match `m`, e.g. `Args<1, 2>(Contains(5))`.|

## Composite Matchers ##

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

|`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`.|
Operation Mode
