I suspect this will be used as an excuse by many not to have their car tested, why bother when you don't need too after all
To save wrangling with slippery insurance companies, who hardly need an excuse to avoid making any type of payment, I would suggest it prudent to have your car tested as per normal.
At the end of the day, an MOT test is not a difficult hurdle to jump if your car is maintained correctly, and fear of catching the lurgy should not be any type of excuse to not venture to the garage to have it done.
After all is said and done, if you are that afraid of leaving the house to have an MOT done, then you shouldn't be out driving your car in any event, so it should be SORNed when the MOT expires.
I for one, provided we are still allowed to leave the house shall be having my MOT carried out at the normal time.
Out of respect for the nominated tester, I would suggest that the car is cleaned thoroughly prior to presenting it for test, and of course it is one of those cases where social distancing is easy to practise.
A lot of small garages will undoubtedly struggle during this period of uncertainty, however the risks, either perceived or real to either you or the garage staff will be considerably lower than for example going to the supermarket.
We should put it into context as consumers, an MOT test takes roughly 40 minutes to complete, and shouldn't be a source of worry at all.
Brian