Lectures and assignments are based on the assumption that you have done this. Testing is usually infrequent and may be cumulative, covering large amounts of material. You, not the professor, need to organize the material to prepare for the test. A particular course may only have 2 or 3 tests in a semester. Makeup tests are often available.
Teachers frequently rearrange test dates to avoid conflict with school events.
Professors in different courses usually schedule tests without regard to the demands of other courses or outside activities. Teachers frequently conduct review sessions, pointing out the most important concepts. Professors rarely offer review sessions, and when they do, they expect you to be an active participant, one who comes prepared with questions. Mastery is usually seen as the ability to reproduce what you were taught in the form in which it was presented to you, or to solve the kinds of problems you were shown how to solve. Mastery is often seen as the ability to apply what you've learned to new situations or to solve new kinds of problems.