I had a Functional Capacity Evaluation, which I am assuming is the same thing you are having.
Take your normal meds the morning of the test. Don't take any PRN meds that you use for breakthrough pain, but take them with you to the test. If you start to hurt after awhile, tell them that you need to take an extra pain med and be specific about what hurts that is causing you to need the extra medication. About halfway through my test I had to take an extra medication. If the next test requires more physical activity, ask them if they can change and do a more sedentary activity to allow the meds time to kick in.
You MUST make a real effort to do the tests they require. At least make an attempt and do as much as you can without hurting yourself. I agree with the other poster, that you need to be very specific about what hurts that is casuing you not to be able to continue with that particular activity. One activity that I did required me to kneel on the floor.....well great...I got down and the tester had to help me up!!
The day after the test I could not get out of bed!!!! I called my doctor who called in a Rx for steroids and documented my pain. I also called the center that did the testing and spoke with the tester about my pain and offered to go in for her to evaluate me. She declined, but again you have documentation of the after effects of the testing. I also let my lawyer know what was going on. You can NEVER have too much documentation!