Mocking non-virtual methods in C++ without editing production code?

I would write a Perl/Ruby/Python script to read in the original source tree and write out a mocked source tree in a different directory. You don't have to fully parse C++ in order to replace a function definition.

There are some different ways of replacing non-virtual functions. One is to re-declare them and compile a new test executable for each different set of non-virtual functions you'd like to test. That's hardly scaleable.

A second option is to make them virtual for test. Most compilers allow you to define something on the command-line so compile your code with -DTEST_VIRTUAL=virtual or -DTEST_VIRTUAL to make them either virtual or normal depending on whether or not it's under test or not.

A third option which may be usable is to use a mocking framework that lets you mock non-virtual functions. I'm the author of HippoMocks (disclaimer with regard to neutrality and so on) and we've recently added the ability to mock plain C functions on X86 platforms. This can be extended to non-virtual member functions with a bit of work and would be what you're looking for. Keep in mind that, if your compiler can see both the use and the definition of a function at one time that it may inline it and that the mocking may fail. That holds in particular for functions that are defined in headers.

If regular C function mocking is sufficient for you, you can use it as it is now.

One approach would be to specify different sources for testing. Say your production target uses rootModule.h and rootModule.cpp. Use different sources for your testing target. You can specify a different header by changing your include path, so that #include "rootModule.h" actually loads unittest/rootModule.h. Then mock rootModule to your heart's content.