A protagonist is the main character and center of the story. Usually, the protagonist is shown facing several difficult events before becoming a better person at the ending of the story. An example of a protagonist is Batman.
An antagonist is the villian or enemy of the protagonist. The biggest obstacle for the protagonist is the antagonist as the antagonist is the greatest rival. An example of an antagonist is the Joker.
First I would go up to them and tell them that its not a good idea to cheat in a test. Second I would record them, or get proof of what they said, Then I'll tell the teacher.