I would have to agree with what Brian said above. Concentrate on your breathing which will give you somthing to occupy your mind, and will give you the benefit of helping your stamina. I know that it helped me a whole lot while doing forms for my black belt test. It is funny how when we feel stress the first thing our body wants to do is start holding our breath. Not sure why this is, but it does happen. The way my instructor taught me to do this was to try to breath in for at least two moves of the form and then breath out for two or so moves. Good luck on your test and please let us know how it turns out!
I'm going to disagree on focusing on breathing. For forms maybe, but not for sparring. Breathing needs to be instinctual, switching the focus to breathing is a bad idea in increases the chance of getting hurt.
In.... Out..... In.... Out... I *thud* gasp..gasp..wheeze..gasp..wheeze...