certain things cannot be applied to older cars ie airbag systems and cats to name a couple, but otherwise, if it's fitted, it's testable. at the end of it all, the MOT is designed to make sure a vehicle is roadworthy (on the day of the test only) and complies to a minimum set of standards.
count yourselves lucky it's not Japan, they have a test every 6 months, and that is tough, hence the large numbers of imported Jap spec cars with low mileage about, it's not uncommon for a car to fail it's test with only 20/30k on the clock over there, and be uneconomical to fix