How to mock templated methods using Google Mock?

Question

I am trying to mock a templated method.

Here is the class containing the method to mock :

class myClass
{
public:
    virtual ~myClass() {}

    template<typename T>
    void myMethod(T param);
}

How can I mock the method myMethod using Google Mock?

Answer 1

In previous version of Google Mock you can only mock virtual functions, see the documentation in the project's page.

More recent versions allowed to mock non-virtual methods, using what they call hi-perf dependency injection.

As congusbongus states:

Google Mock relies on adding member variables to support method mocking, and since you can't create template member variables, it's impossible to mock template functions

A workaround, by Michael Harrington in the googlegroups link from the comments, is to make specialized the template methods that will call a normal function that can be mocked. It doesn't solve the general case but it will work for testing.

struct Foo
{
    MOCK_METHOD1(GetValueString, void(std::string& value));

    template <typename ValueType>
    void GetValue(ValueType& value); 

    template <>
    void GetValue(std::string& value) {
        GetValueString(value);
    } 
};

Answer 2

Here is the original post again with comments to aid in understanding:

    struct Foo 
    { 
        // Our own mocked method that the templated call will end up calling.
        MOCK_METHOD3(GetNextValueStdString, void(const std::string& name, std::string& value, const unsigned int streamIndex)); 

        // If we see any calls with these two parameter list types throw and error as its unexpected in the unit under test.
        template< typename ValueType > 
        void GetNextValue( const std::string& name, ValueType& value, const unsigned int streamIndex ) 
        { 
            throw "Unexpected call."; 
        } 
        template< typename ValueType > 
        void GetNextValue( const std::string& name, ValueType& value ) 
        { 
            throw "Unexpected call."; 
        } 

        // These are the only two templated calls expected, notice the difference in the method parameter list. Anything outside
        // of these two flavors is considerd an error.
        template<> 
        void GetNextValue< std::string >( const std::string& name, std::string& value, const unsigned int streamIndex ) 
        { 
            GetNextValueStdString( name, value, streamIndex ); 
        } 
        template<> 
        void GetNextValue< std::string >( const std::string& name, std::string& value ) 
        { 
            GetNextValue< std::string >( name, value, 0 ); 
        } 
    };