Easiest way of unit testing C code with Python

Using ctypes would be my first instinct, though I must admit that if I was testing C code that was not going to be interfaced from Python in the first place, I would just use check. Check has the strong advantage of being able to properly report test cases that segfault. This is because it runs each test case in a separate process.

Now if you are going to create a python wrapper for the C code anyway, I would simply unittest the wrapper. In addition to the methods you listed above, you could also use Cython to write such a wrapper with python-like code and then unittest it from Python.

I think that the exact solution depends on your code. Not all libraries are easily suitable for wrapping as a DLL. If your is, then ctypes is certainly the easiest way - just make a DLL out of your library and then test it with ctypes. An added bonus is that you now have your library conveniently wrapped as a standalone DLL which helps to decouple your application.

Sometimes, however, a more thorough interaction will be required between your C code and the testing Python code. Then, it's probably best to hook it as an extension, for which SWIG is a pretty good tool that will automate away most things you'll find boring about the process.