I had mine recently, they check your height & weight, test your hearing, check your eyes(not as thorough as the opticians), blood pressure, blow into this (lung capacity)
They test your urine for sugar & protein levels. The doc looks in your eyes and ears, checks you have cold wet nose and nice shiny coat.
Looks at your joints, listens to your heart and lungs, drop and cough if applicable.
All you can do is turn up clean and ontime, you can't do anything to change your medical fitness so there's no point worrying about it.
Yeah, they get you to strip off so clean shreddies are just good manners!