Everything: Engine, frame, gear box, fuel tank, exhaust pipes, CO levels, noise levels, battery & electricity, windshields and windows, bodywork (including the bottom of the vehicle), mirrors, lights, wheels, brakes, steering, dampers, horn, bumpers, safety belts, plates, documentation… yes, everything, my advice, if the car isn’t new take it to a garage and make a Pre-ITV review
I’m not an expert, just passed my wife’s car ITV two weeks ago!!! 😉
Cesar