I'm going to refuse to help someone on a test.
Are they asking you to help them cheat?
I think he is going to ask me again for help for this big project after failing the last one.
It is wrong to help people cheat if they don't study. You should try to help them study instead before if they ask for help.
Why should I take the time out of my day to help him study when I don't have time for my own shit?
It is definitely not your responsibility whether your friend passes the test or not. If you are busy yourself, let them know that you don't have the time right now to help because you have to take care of your own responsibilities.