A Test

Today, I got back one of the four tests that I took last week. It was by far the hardest test that I took last week and one of the hardest tests I have ever taken at Clemson apart from Accounting 202. As my professor put the grade distribution on the board, it was evident that about half the class had received a D or lower. This obviously is not a good distribution. He very casually begins talking about how, yes the first test is always hard. Most all of the multiple choice I put on the test are really hard and I don't expect you to get a lot of them right. He claims that he likes to use tests to find what we are having difficulty with in the course. WHAT?!? Aren't tests suppose to test the knowledge that you gain from the course, so you can prove what it is you do know? I believe the professor should give some type of quiz or something before the test to find out what we are struggling with. I think it is entirely unfair to make a test AS DIFFICULT as possible just to see how difficult the material is for your students. This is a service marketing class and there is no reason it needs to be this difficult. This is mostly to vent my frustration but also to pose the following question...

What is the purpose of a test? Should it test the knowledge you have learned? Should it try to find out what you didn't learn? Should it help you apply what you learned? Or some combination? or none of the above?