According to a short piece in the January 27 Science (p 437), not only do tests assess student learning and encourage student learning, but they help students remember the material. Students studied for a test (TOEFL, Test of English as a Foreign Language), then were either tested or allowed to study again. They were then tested on how well they remembered the material. The study-study people remembered more initially, but the study-test group did better after a week.
So welcome those midterms!