Mock non-virtual method C++ (gmock)

Question

I have class

class CSumWnd : public CBaseWnd
{

 private:
 bool MethodA()
}

Please can you help how to mock MethodA() without making virtual, I didn't understand the concept of hi-perf dependency injection

Answer 1

It means you will have to templatize your production code. Using your example:

CSumWind class definition:

class CSumWnd : public CBaseWnd
{

 private:
 bool MethodA()
};

Mocked CSumWnd class definition:

class MockCSumWnd : public CBaseWnd
{

 private:
 MOCK_METHOD(MethodA, bool());
};

Production class which have to be tested with mocked class CSumWind . Now it becomes templated to provide using CSumWind class in production code and MockCSumWnd class in tests.

template <class CSumWndClass>
class TestedClass {
//...
   void useSumWnd(const CSumWndClass &a);

private:
  CSumWndClass sumWnd;
};

Instantiation of TestedClass in production:

TestedClass <CSumWnd> obj;

Instantiation of TestedClass object in test executable:

TestedClass <MockCSumWnd> testObj;

Answer 2

If you don't want to change the existing code, here is a specific solution for VC++ I'm working on ( https://github.com/mazong1123/injectorpp ). The brief steps are:

1. Leverage DbgHelp.h to retrieve all methods' symbols and memory addresses of a class. Basically it retrieves meta info from .pdb file at runtime.
2. Compare the user input to-mock method symbol with step 1's output, get the to-mock method's memory address.
3. Leverage windows api WriteProcessMemory to change the entry bytes of the to-mock method, that is something similar as: __asm {move eax, 1; ret}.

Let's put key code here.

1. Retrieve methods' symbols and addresses of a class. Below is the key idea of the implementation. The full source code is availiable at https://github.com/mazong1123/injectorpp/blob/master/injectorpp/ClassResolver.cpp

    // Retrieve class symbol. if (SymGetTypeFromName(this->m_hProcess, modBase, className.c_str(), classSymbol) == FALSE) { throw; } // Get children of class - which are methods. DWORD numChildren = 0; if (SymGetTypeInfo(this->m_hProcess, classSymbol->ModBase, classSymbol->TypeIndex, TI_GET_CHILDRENCOUNT, &numChildren) == FALSE) { throw; } // Get methods info. if (SymGetTypeInfo(this->m_hProcess, classSymbol->ModBase, classSymbol->TypeIndex, TI_FINDCHILDREN, methods) == FALSE) { throw; } // Retrieve all methods. for (DWORD i = 0; i < numChildren; ++i) { ULONG curChild = methods->ChildId[i]; // Resolve function. Function resolvedFunction; this->m_functionResolver->Resolve(classSymbol->ModBase, curChild, resolvedFunction); // Add the resolved function to the output. resolvedMethods.push_back(resolvedFunction); } 

2. Step 2 is trival. It's only text comparing and processing.

3. How to inject the magic asm to change the method behavior: (The full source code is available at https://github.com/mazong1123/injectorpp/blob/master/injectorpp/BehaviorChanger.cpp )

    // A magic function to change the function behavior at runtime // // funcAddress - The address of the function to be changed from. // expectedReturnValue - The return value should be changed to. void BehaviorChanger::ChangeFunctionReturnValue(ULONG64 funcAddress, int expectedReturnValue) { // The purpose of this method is to change the return value // to what ever int value we expected. // Therefore, we just need to inject below asm to the header of specific function: // // mov eax, expectedValue // ret // // Above asm code tells the function to return expectedValue immediately. // Now let's prepare the asm command. byte asmCommand[6]; // mov asmCommand[0] = 0xB8; // The value. asmCommand[1] = expectedReturnValue & 0xFF; asmCommand[2] = (expectedReturnValue >> 8) & 0xFF; asmCommand[3] = (expectedReturnValue >> 16) & 0xFF; asmCommand[4] = (expectedReturnValue >> 24) & 0xFF; // ret asmCommand[5] = 0xC3; WriteProcessMemory((HANDLE)-1, (void*)funcAddress, asmCommand, 6, 0); } 

Answer 3

Try CppFreeMock and some others mentioned here .

Example:

string func() {
    return "Non mocked.";
}

TEST(HelloWorld, First) {
    EXPECT_CALL(*MOCKER(func), MOCK_FUNCTION()).Times(Exactly(1))
        .WillOnce(Return("Hello world."));
    EXPECT_EQ("Hello world.", func());
}