I would think you'd want to treat it as a normal day doing what you would normally do. If you are exercising just to bring it down just for the test you are doing yourself a disservice on a true evaluation.
Keep in mind as well, that for some people with diabetes, exercise will temporarily raise blood sugar. There is no point in trying to "pass" a blood test. What you want is a realistic number, not a "cooked" one so that you can get the proper course of treatment.