Unit Testing for c Library

This question is an extension to this question. I am using a Nmatrix a Fast Numerical Linear Algebra Library for Ruby.

It uses ruby wrappers around c code to for many functions such as Singular value decomposition etc.It is very easy to test ruby code which usually makes calls to c for speed but their is no way to test c code.

I want to write an automated test suite for NMatrix C API.I have used the library check but only for basic c functions. I know that their are good libraries for this like cmocka.

I am a newbie to open source and i wanted to ask what would be the best way to actually add a c testing library to existing NMatrix project? Can you recommend some tutorials to link two libraries (i.e. an original library and a testing suite.) ?

Obviously i must have free permission to use the testinglibrary in my project without causing any legal issues.