This is gen, from someone who works at OASC.
If you are assessed as TU it normally means a specialist medical opinion is required. The Candidate will normally complete the selection process, assuming you pass the interview & aptitude tests.
Only if you are selectable in the long term will a specialist medical appointment be made. It saves money etc.
If you are unfit to complete the fitness test due to a cold or recent injury, then you can be asked to return at a later date when you are fit to take the test.
WTN