What files are linked in an mbed OS 5 project?

I'm writing an external library (a component controller) for use with mbed 5 and plan to make it available in the mbed repositories. I want to write tests to confirm that my code is working properly, but they're just regular ordinary unit tests and don't need to be run on an embedded controller. I'm looking at Catch as my framework, which provides a main for the test suite.

When I build my project with the mbed CLI or Eclipse CDT (using an exported project), what .cpp files are included, and what .o files are linked into the embedded image? Does the image only include code pulled in from my main.cpp file via includes, or does it compile and link all of the .cpp files visible (potentially including my test cases)? If the latter, is there a clean way to exclude them that won't collide with the built-in utest functionality?