Say I'm in a class, learning some difficult topic. I know there will be a test, and the test will make up a big chunk of my grade (maybe all the tests together are most of my grade). I know the test will be such that passing it is easiest if I memorize — because that's how tests are. What do I do?

This is not usually true in the context of physics. I recently taught a physics course, the final was 3 questions, the time limit was 3 hours. Getting full credit on a single question was enough for an A. Memorization fails if you've never seen a question type before.