You're right the reverse lights are not a testable item, as for the fualt possibly the switch but that's only a guess!!! You really need to test the switch by bypassing it with a bit of wire but not familiar with the Clio so can't advise oyu on how to find the switch.
Now I think I know the answer to this and it is NO. However, please can somebody confirm that reverse lights are not tested on an MOT?
I noticed last night mine weren't working. I changed the bulbs and still not working. The fuse is OK as other things on the same fuse are working fine.
Regardless of the MOT question, what is it likely to be? I guess some sort of switch when I select reverse gear? If so, what sort of repair job is this? Easy, cheap etc. I have a 2003 Renault Clio.