1.) You are given a test at school that has questions that teacher hasn't covered yet. In the middle of the test you notice that your friend next to you has a cheat-sheet. The teacher doesn't notice.
Ask to share the cheat-sheet. This test isn't fair, so why should you be?
Good for them, they beat the system.
Confront them after the test and try to convince them not to cheat anymore. You don't want them to get in trouble.
Confront them after the test and force them to tell the teacher they cheated, or you will tell on them. They must pay for their misdeeds.
Inform the teacher right in the middle of class that they are cheating. Cheaters never prosper!