I want to refer to people who have completed a short written exercise. "Graduate" would be one way, but that seems a little over the top. "Completer" would be another, but that's ambiguous as a completer could be something that helps you to complete. Any ideas?
A nice unambiguous term is those who have completed the test.
However, finisher is often used for those who have crossed the finish line in a race, and may work in your case.