An old instructor of mine would always have fun with the lower grades being tested by asking for a technique he new they hadn't covered (or at least couldn't do). The reason for this wasn't to make them look stupid but to see their reaction. People that stood there and fluffed generally failed but those that would just do whatever technique came would usually pass.
A thing to keep in mind (once you've done the practise) is that the testing is not just about doing a set of techniques on someone that attacks - it's a chance for your instructor to see how you cope under pressure.
So, once you're happy with performing the techniques to a suitable standard, just relax and live in the present.
Also remember, it makes no difference if you pass or fail the test in that you're still going to be exactly the same standard in aikido (i.e. improvement is through training, not through awards).