I don't think they would intentionally tell you that you didn't have to do something and then make you do it on the day, that would be unfair. The main thing with the COMPASS test is to brush up on your mental maths, basic physics (if doing the basic COMPASS), and maybe some memory exercises to help recall info. The other parts you can't really prepare for to be honest. So maybe just put a little time aside for this during your prep, and if you are made to do it then you'll be prepared in some way.
