I agree that once the tests start if you have prepared for it you'll do fine.
My first black belt test was myself and a guy going for brown belt. In my instructors dojo (his garage) with 8 black belt board members, my family (brother, sister brother in law, my father and mother (this was the first test they had ever been to) and the other black and brown belts who would be used in the self defense and sparring phase of the exam. All crammed into a two car garage (20X20). You would think it would have been nerve racking seeing everyone that close, but I didn't see a thing, I was to busy trying to survive and not screw up to worry about anything.
In our system brown belt was the hardest test before black, the most physically demanding and nerve racking. What a great time to have that test before the other black belts. Cause you know that everyone of them had to do the same and they are all pulling for you, since they know what you are going through.
Like the NIKE commercial, JUST DO IT! You'll be fine.
Mark