I realize that accusatory turnabout is a fun exercise, but what you have here only meets the form of turnabout, and not the substance. One of the key indicators that you've gone off the rails: your turnabout necessitates conceptual contortions in order to make a false equivalence.

In your post above, you falsely claim that the students are being accused of plagiarism. They are not. While plagiarism can be a kind of academic dishonesty, it is not the particular kind of academic dishonesty at issue here. Then, to complete your false equivalence, you try to re-frame the de rigueur practice of drawing test items from an item bank as plagiarism, which is just laughable and ignores both the purpose of the test instrument and the different roles of student and teacher.

I contest that the professor is too.

The word "contest" in the above context means "to oppose as mistaken or wrong". So your sentence literally reads that you dispute that the teacher is also cheating. Clearly you have been arguing the opposite.

I think it might be time to give it a rest.