Don't study immediately prior to test. Relax or do something unrelated to the test. During the Test Do something different. Tense and relax muscles in several parts of your body, then take several deep breaths with your eyes closed. I'm going to feel calm and relaxed.
Anxiety is created by expectations or thoughts about what is likely to happen.
If you say negative things to yourself about your abilities, it produces a corresponding negative emotional reaction, anxiety. Your beliefs about something create expectations about how a situation will play out. For example, if you believe you are not smart, don't know the information well enough, or aren't capable of performing well on exams, then your expectations will be for failure. Negative expectations then create anxiety and the anxiety will disable you from actually doing well. Therefore, if you believe in yourself and your abilities, and thus have positive expectations for how you will perform on the exam, you may negate most of the anxiety.