There is no requirement to test ring continuity on a MWC.
Although the minor works certificate does not contain any special point where you have to say you have tested that a ring main is intact it does ask you to sign that:-
“I/We CERTIFY that the said works do not impair the safety of the existing installation, that the said works have been designed, constructed, inspected and tested in accordance with BS 7671:2008 (IEE Wiring Regulations)”.
And in BS7671:2008 it says 612.2.2 Continuity of ring final circuit conductors
A test shall be made to verify the continuity of each conductor. including the protective conductor. of every ring final circuit.
Also it states on the form:-
“The relevant provisions of Part 6 (Inspection and Testing) of BS 7671 must be applied in full to all minor works.”
Since it could be a radial circuit, it of course will not list tests that may not be required.
Since the Earth fault loop impedance is required on the form this would change quite a bit if a ring was made into a couple of radials so it would be a very quick test to see if it was wired as a ring or double radial when the original tests were made.
As to the original post although he should issued a minor works for all work in the real world it is not really required and not worth £20 or too much hassle and I will guess the guy did not want to get out all the test equipment for such a simple job.
So I would not worry about it.