internal working of strace

I want to know the internal working of Strace . What does each directory and .c file represent in http://ift.tt/2f3sCa4 . How to add a test to the already available tests in http://ift.tt/2CwuTHx and it would be better if an example is provided. Also, basically what are IOCtl decoders and how to add tests for them.