Ab initio do a standard compass test. AE applicants do the Advanced compass test.
Check this link as it outlines what to expect. The main thing would be to brush up on your maths, memory and basic physics as the other bits can't really be prepared for. Actually, it would probably be more important to get a good nights rest beforehand as the test is very draining.
Ab initio
European Pilot Selection & Training, Compass
Advanced Entry
European Pilot Selection & Training, Advanced Compass
Johnson, just be patient, if they say they will call you back within 2 weeks, they will. They are normally very swift to tell people if they fail, so generally speaking, no news is good news - in most cases anyway.