Understanding What to test

[strikeouts27]

So I completed this hacking.py python game and I was told that I need to write tests afterwards. I am starting to recognize that I should have written tests as I was working but what is done is done and I cannot change the past.

https://github.com/strikeouts27/python_hacking_game

Can anyone offer me suggestions on what people would expect me to test? I have never written tests before.