In short, they use your unit test (even without asserts), to test against potential issues from their upcoming release. First they run all your test on its current version, then they run them again using the new version, its not important that the test pass or fail, but that the do no...
When you get closer to your exam, ask a parent, friend, or your teacher to quiz you over the information. You can create example questions for them to ask you, have them question you from the review, or let them question you from your notes. This will show you if you need to review...