Seriously, I have about 6 tests a week for my subjects, if anything they detract you from studying and you waste time which could actually be used for learning. I'm not saying to have no tests, but there are way too much!
Although 6 tests a week is a little much, I personally am actually quite grateful for tests.
1. They force you the really study (instead of procrastinate).
2. They give you great practice for actual SACs (the question style, honing in on the little things that lose 1 or 2 marks etc.)
3. They're great for the teacher to see how you're actually going with the content.
4. They're great for yourself to check your improvement and what you can expect for your next SAC.
I do so much reading for philosophy/renaissance that a test really forces me to take a step back, look at the concepts and gain a concrete understanding instead of just waffling about with 100's of pages of reading. It's also a great bridge between the overload of information/content and important assessments.