How to mock a template method that's in a template class in GTest?

Question

I want to mock myFunction in google test and am having issues with the two templates.

template <class Outer>
class MyClass{
   template <class T>
   void myFunction(const int a, T * b);
};

Answer 1

First of all, Outer template type isn't an issue here since it is not used in myFunction signature.
To handle type T you will need to fully specialize mocked method for all types used during testing.
Imagine you want to test that method with T=std::string:

template <class Outer>
class MyClassMock {
public:
    MOCK_METHOD(void, myFunction, (const int, std::string*));

    template <class T>
    void myFunction(const int a, T* b);

    template <>
    void myFunction(const int a, std::string* b)
    {
        myFunction(a, b);
    }
};

If your tested function will have signature like this:

template <typename TMyClass>
void UseMyClassWithString(TMyClass& i_value)
{
    std::string t;
    i_value.myFunction(5, &t);
}

Result test may looks like this:

TEST(UseMyClass, ShouldCallMyFunction)
{
    MyClassMock<size_t> mock;
    EXPECT_CALL(mock, myFunction).Times(1);
    UseMyClassWithString(mock);
}

Here your Outer type is size_t and it is used only to create mock object.