A number of riders I talk to are resistent to doing a fitness test. Maybe it's the name, "test," that gets them nervous. What else could we call it? Evaluation? Assessment? Masochism? OK, maybe that last one's not helping.
It seems some riders want to be in peak form before they do a fitness test. Get over it. Do the test already. It's probably better training than you do most of the time and the purpose is to assess your current fitness—not your ideal performance—in order to improve your training. It's not so you can tell your friends how much you bench (power is today's cycling equivalent of the meathead weightlifter talk).So if you have a fear of doing a fitness test, do like I said: get over it and do the test already. If you think that disappointing numbers are going to ruin your future in cycling, you need a shrink not a training plan. So instead, use the data from the test to determine where you are now, how your current performance compares to a similar time last season, and what you can do to improve your performance for the future.
There are lots of fitness tests out there. If your coach prescribes one, follow those directions closely. If you're doing your own, just pick one and stick with it so you can compare your results over time. Two popular training books, The Cyclist's Training Bible by Joe Friel and Training and Racing with a Power Meter by Allen & Coggan each describe some assessments.
In short, use a fitness test to challenge yourself and plan your move forward. Save the psyching out for your competition at the races.