The idea of the class is to teach you and give you the information needed to pass tests. A
huge test would cover most of the things that have been covered in the class. If you don't know most of these things, and can't pass the test, then you shouldn't pass the class.
One test does not define a student completely. A student could do really well on all, or most, of their assignments, but could maybe mess up on that test. It could be that the person is not feeling too go that day because sometimes people do not feel at their best.
Empirical evidence shows that large and cumbersome tests are not effective. Making student's lives stressful to the point of suicide is not the way to go, and Japan and South Korea very much prove this. We should look to countries like Finland and Denmark for real educational reform. If we want to be guided by evidence, anyway.