Need suggestion for running modified source code

I am new to opencv and cmake. I really need some instructions on building modified source code. I cloned master branch from github. I modified ` opencv/modules/imgproc/src/grabcut.cpp` and wants to write another class lets say `class run_grabcut` in `opencv/test.cpp` using the modified version. Would you please give me 2 examples: 1. what files should I include in the source code `opencv/test.cpp`? 2. Which `CMakeList` should I modify to build a `test.cpp` target so that I can only run this file? Would you please give me an example of this CMakeList? Thanks so much for your help!