"They said the MOT had to be done on the car as it came in from the street".
Hmmm. I suppose if you only say to a garage "I want an MOT test" they're then correct in doing exactly that before anything else.
However I take my car into my excellent local garage and say "Please get my car through the test", which means that I expect them to check it over thoroughly first, and then correct any faults, before actually putting it in for its test. (They can't actually test it straight away anyway because they're not a test centre; they have to take it to a neighbouring workshop to get the test done).
You could reasonably argue that they should have done the service first but you'd probably have ended up VERY annoyed if they'd then found a major fault at the MOT stage, meaning that it was uneconomic to repair your car, as you'd then end up paying for a service on a car which was simply heading off to the scrap yard.
So, as I see it, since you didn't specify that you wanted a pre-MOT check carried out, the garage did the correct thing. It's not as if it cost you anything, since there's no charge for a MOT re-test (relating to a wiper fault) if it's carried out at the same garage before the end of the next working day:
https://www.gov.uk/getting-an-mot/retests