I wish I as a student had this power. I took an exam once for a class I had taken before (transfer student woes). I went into the hall, took the easy exam, turned it in, and left. They lost my test.
I had no idea until 3 weeks later when exam scores were finally uploaded and mine was missing. The quarter was over and what the hell could I possibly do at that point? I had no possible evidence to give to show that I not only took the test but definitely passed because I've already taken the class
When I was at university you returned the test and singed on shared list that you had participated. So if your name was on the list it was proof that you were at least in the room at the time. Probably more so done to track registrations vs participation but would also help in these situtations.