bitcoincore development – How does bitcoin functional test framework work?

Could someone explain how and where in the code the bitcoin test framework calls map to C++ bitcoin core code or RPC calls such that regression suite tests the bitcoin core functionality?

Background and more details
I am writing a blockchain application and was thinking of how I can do regression while I keep developing. I wanted to leverage the design used by bitcoin (or any other blockchain application). I would expect that framework would call either C++ classes in bitcoin core directly or use RPC from python scripts such that features are tested.

I spotted that bitcoin functional tests are written in python scripts whereby calls a bunch of scripts testing specific features But I cannot spot in the bitcoin framework as to where it eventually calls actual bitcoin core c++ code or RPC.

Appreciate your help in spotting the code in python scripts in the framework that does it.