That is true, but the problem shows up even with open-ended tests. In my country, we generally don't use tests/quizzes, and nevertheless, every year, many stude

That is true, but the problem shows up even with open-ended tests. In my country, we generally don't use tests/quizzes, and nevertheless, every year, many students attempt to cheat – and some of them undoubtedly get away with it. Regardless, I agree, attempting to assess the progress of a cheater is a fool's errand.