[bluGill]

I have done things like that, but the one definition rule gets in the way.

    void DoSomething(widget* param, OtherClassWithvirtual* param2) {...}

My DoSomething function needs to link to widget, but now I have two different libraries that widget could be in. The linker encodes in my binary which library to load to get widget. All attempts to use the other library instead are undefined behavior.

The only way I know of to work around that is build DoSomething twice, linking the real widget once and the test widget the other. Note that DoSomething takes two parameters, and those are classes that may themselves also take other classes with virtual functions. All the possible cases quickly gets into a combinatoric explosion and my build times goes from an hour (already way too long) to days.

If I'm wrong please tell me how, I'd love to not have so many interfaces just because someone doesn't want their unit test to become a large scale integration test.