An MOT is a safety and emissions check, not a health check on the whole car. The tester looks at brakes, steering, suspension, tyres, lights, mirrors, wipers, seatbelts, the exhaust and the structure of the car.
The most common failures are simple things: a blown bulb, worn tyres, wipers that smear, or a screen wash bottle that is empty. Checking those the night before can save you a wasted trip.
Our full checklist and what happens on the day are set out on the MOT testing page.
An MOT does not check the clutch, the gearbox or the engine's general condition — that is what a service is for.