Testing can be an effective way to evaluate your progress and highlight what you need to work on.
To prepare for testing I suggest the following:
Consistent training. Would you run a half marathon without training? I did 15 years ago. My time was horrible and I could barely walk for a week. People who train sporadically sometimes try to “cram” last minute for a test. This doesn’t work, especially at higher levels. As the test goes on and you become physically and mentally tired your lack of preparation shows. Instructors are not fooled. Train consistently and allow yourself to develop over time.
Train Under Stress. As mentioned above, fatigue and the stress of being evaluated can challenge your ability to perform. To prepare, train under stress.
Know Your Stuff! If the instructor asked you why you elbowed instead of punched and you answer with a blank stare that is not a sign you are prepared. You need to know why you are doing what you are doing. E.g. The attacker was too close to punch so I elbowed. Good answer!
Practice Controlled Aggression: I have seen tests where candidates have repeatedly hit each other (lack of control) and others where people’s strikes resembled pillow fluffing more than strikes. You must convince the instructor that the techniques could work in real life. You have to do this while not injuring your partner (grounds for failure).
You want to enter a test prepared physically and mentally. Don’t try to rush through the levels and ask your instructor for tips.