Question

I am a fairly new software developer currently working adding unit tests to an existing C++ project that started years ago. Due to a non-technical reason, I m not allowed to modify any existing code. The base class of all my modules has a bunch of methods for Setting/Getting data and communicating with other modules.

Since I just want to unit testing each individual module, I want to be able to use canned values for all my inter-module communication methods. I.e. for a method Ping() which checks if another module is active, I want to have it return true or false based on what kind of test I m doing. I ve been looking into Google Test and Google Mock, and it does support mocking non-virtual methods. However the approach described (https://google.github.io/googletest/gmock_cook_book.html#MockingNonVirtualMethods) requires me to "templatize" the original methods to take in either real or mock objects. I can t go and templatize my methods in the base class due to the requirement mentioned earlier, so I need some other way of mocking these virtual methods

Basically, the methods I want to mock are in some base class, the modules I want to unit test and create mocks of are derived classes of that base class. There are intermediate modules in between my base Module class and the modules that I want to test.

I would appreciate any advise!

Thanks,

JW

EDIT: A more concrete examples

My base class is lets say rootModule, the module I want to test is leafModule. There is an intermediate module which inherits from rootModule, leafModule inherits from this intermediate module.

In my leafModule, I want to test the doStuff() method, which calls the non virtual GetStatus(moduleName) defined in the rootModule class. I need to somehow make GetStatus() to return a chosen canned value. Mocking is new to me, so is using mock objects even the right approach?

Answer 1

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.

Answer 2

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.

Answer 3

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.

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