python3 src/test_SerialSevenSeg.py
There are a bunch of other test files. test_Serial will work without music and the seven seg. Though it'll have issues if the i2c devices aren't connected.
Pong.py is the main game class which deals with instantiating all the of the game objects and the update / render functions. Look at Game.py to see the parent type. Should be pretty easy to make other games using Game.py and GameObject.py and the other classes around it.