P.S. Apologies, I’m relatively new into testing and C++, so forgive me for any obvious mistakes.

Let’s say I have these files (Please disregard the lack of header files here.)

A.hpp

namespace A {
    namespace upper {
        void func1();
    }
}

B.hpp

namespace B {
    namespace lower {
        void func2();
    }
}

A.cpp

namespace A {
    namespace upper {
        void func1() {
            B::lower::func2();
        }
    }
}

B.cpp

namespace B {
    namespace lower {
        void func2() {
            cout << Actual B called;
        }
    }
}

Now, normally calling A::upper::func1() should display “Actual B called”. However I do not want to call the Actual B, I want to be able to mock it. At this point the source code cannot change without significant refactoring. Is there a way to mock out this call using GMock?

I tried overriding B

Test.cpp

namespace B {
    namespace lower {
        void func2() {
            cout << Mock B called;
        }
    }
}

int main() {
    B::lower::func2();
}

I am getting these errors

Error LNK2005 “void __cdecl B::lower::func2(void)” (?lower@0B@@YAXXZ) already defined in B.obj TestOverrideForMock 1

Error LNK1169 one or more multiply defined symbols found TestOverrideForMock 1