The whole point of testing is to put them in hypothetical situations and grade their progress with purpose of being aware of their development so we can improve it. Another thing we do is selecting the particularly good ones for further advanced training.
The problem with cheating is that it provides wrong data about their progress, you don't want to end up with a generation that cheated their way up without learning anything.
The selection for further training is probably not that big of a problem, its mostly about supply and demand and ChatGPT won't change that.