# gMock Cookbook
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You can find recipes for using gMock here. If you haven't yet, please read
[this](for_dummies.md) first to make sure you understand the basics.
**Note:** gMock lives in the `testing` name space. For readability, it is
recommended to write `using ::testing::Foo;` once in your file before using the
name `Foo` defined by gMock. We omit such `using` statements in this section for
brevity, but you should do it in your own code.
## Creating Mock Classes
Mock classes are defined as normal classes, using the `MOCK_METHOD` macro to
generate mocked methods. The macro gets 3 or 4 parameters:
```cpp
class MyMock {
public:
MOCK_METHOD(ReturnType, MethodName, (Args...));
MOCK_METHOD(ReturnType, MethodName, (Args...), (Specs...));
};
```
The first 3 parameters are simply the method declaration, split into 3 parts.
The 4th parameter accepts a closed list of qualifiers, which affect the
generated method:
* **`const`** - Makes the mocked method a `const` method. Required if
overriding a `const` method.
* **`override`** - Marks the method with `override`. Recommended if overriding
a `virtual` method.
* **`noexcept`** - Marks the method with `noexcept`. Required if overriding a
`noexcept` method.
* **`Calltype(...)`** - Sets the call type for the method (e.g. to
`STDMETHODCALLTYPE`), useful in Windows.
### Dealing with unprotected commas
Unprotected commas, i.e. commas which are not surrounded by parentheses, prevent
`MOCK_METHOD` from parsing its arguments correctly:
```cpp {.bad}
class MockFoo {
public:
MOCK_METHOD(std::pair<bool, int>, GetPair, ()); // Won't compile!
MOCK_METHOD(bool, CheckMap, (std::map<int, double>, bool)); // Won't compile!
};
```
Solution 1 - wrap with parentheses:
```cpp {.good}
class MockFoo {
public:
MOCK_METHOD((std::pair<bool, int>), GetPair, ());
MOCK_METHOD(bool, CheckMap, ((std::map<int, double>), bool));
};
```
Note that wrapping a return or argument type with parentheses is, in general,
invalid C++. `MOCK_METHOD` removes the parentheses.
Solution 2 - define an alias:
```cpp {.good}
class MockFoo {
public:
using BoolAndInt = std::pair<bool, int>;
MOCK_METHOD(BoolAndInt, GetPair, ());
using MapIntDouble = std::map<int, double>;
MOCK_METHOD(bool, CheckMap, (MapIntDouble, bool));
};
```
### Mocking Private or Protected Methods
You must always put a mock method definition (`MOCK_METHOD`) in a `public:`
section of the mock class, regardless of the method being mocked being `public`,
`protected`, or `private` in the base class. This allows `ON_CALL` and
`EXPECT_CALL` to reference the mock function from outside of the mock class.
(Yes, C++ allows a subclass to change the access level of a virtual function in
the base class.) Example:
```cpp
class Foo {
public:
...
virtual bool Transform(Gadget* g) = 0;
protected:
virtual void Resume();
private:
virtual int GetTimeOut();
};
class MockFoo : public Foo {
public:
...
MOCK_METHOD(bool, Transform, (Gadget* g), (override));
// The following must be in the public section, even though the
// methods are protected or private in the base class.
MOCK_METHOD(void, Resume, (), (override));
MOCK_METHOD(int, GetTimeOut, (), (override));
};
```
### Mocking Overloaded Methods
You can mock overloaded functions as usual. No special attention is required:
```cpp
class Foo {
...
// Must be virtual as we'll inherit from Foo.
virtual ~Foo();
// Overloaded on the types and/or numbers of arguments.
virtual int Add(Element x);
virtual int Add(int times, Element x);
// Overloaded on the const-ness of this object.
virtual Bar& GetBar();
virtual const Bar& GetBar() const;
};
class MockFoo : public Foo {
...
MOCK_METHOD(int, Add, (Element x), (override));
MOCK_METHOD(int, Add, (int times, Element x), (override));
MOCK_METHOD(Bar&, GetBar, (), (override));
MOCK_METHOD(const Bar&, GetBar, (), (const, override));
};
```
**Note:** if you don't mock all versions of the overloaded method, the compiler
will give you a warning about some methods in the base class being hidden. To
fix that, use `using` to bring them in scope:
```cpp
class MockFoo : public Foo {
...
using Foo::Add;
MOCK_METHOD(int, Add, (Element x), (override));
// We don't want to mock int Add(int times, Element x);
...
};
```
### Mocking Class Templates
You can mock class templates just like any class.
```cpp
template <typename Elem>
