The tips above are great especially the be prepared part. As mentioned, taking a last look over notes the day and night before the test. I never look over them again the day of the test.

The other thing that helps is that I get there early so I don't worry about missing it, and I read something like a novel, mystery, light book, or magazine to distract me from the panic. By changing gears for the moment to something unrelated to the test subject, I tend to go in more refreshed and relaxed.

Also during the test, I make sure I read the full question and all the answers 2 times before answering. It helps quell any panic if unsure the first time reading it through and to make better decisions by taking your time.

This may sound silly but it has been shown to help, chewing mint gum or using a mint lozenge, helps calm and stimulate mental capacity for recall.

Best wishes.