If your car fails the MOT test you will be issued with a refusal notice with a list of the issues that need to be addressed. If the garage performing the test is able to offer repairs then you may be able to book the car in for those repairs immediately with a view to retesting the car as soon as possible. There are some MOT centres, however, that are not able to offer repair work, in which case you will need to take the car elsewhere for the remedial work.
Many garages offer a free re-test so customers do not have to pay for the test twice. If the car is tested again within 10 days the car will only be subject to a partial re-test covering the points that failed on the first test. In some cases a garage may charge a partial fee to cover this test depending on the work carried out and the time the partial test takes. Once the car has been repaired the tester will then be able to pass the car.