I've only taken two ranking tests, but found that even though I was not nervous before the tests when I stepped on the mat it was a different ballgame.
The weird thing about this is that I've seen emergency room doctors, police, & prosecuting attorneys...people who deal with actual-real- world-someone-might-die-or-lose-their-freedom-because-of-my-actions kind of stress freeze up when taking a martial arts test (rokyu or gokyu at that) that doesn't make one lick of difference in the outside world. Passing that test isn't going to get you a raise, or a better house, or a better school for your kids. It's not going to make you a better person or make people like you better. It doesn't really gain you anything. Yet so many people always let themselves get freaked out by it. I find this strange.
Ok, I'm rambling now. I've been up a long time so I'll shut up now.