have a look at the manual then with a bit of knowledge you can ask him why he thinks it is a fail and you can question his reply.I had one try to fail the wifes beetle because of a blue neon washer jet so informed him he was wrong so he did a search of the manual and after about 10 mins he huffed and said well it has failed on the brakes, I never went back so they lost 4 mot tests a year and it passed at another station I should have asked for a VT17  complaint form but did not bother.
mot testers cannot even remove parts that are secured to check behind it, that is why so many bay windows fitted with belly plates have no chassis left but still pass.

wiper blades that are starting to break away at the ends are not a failure as long as they clear the screen as the VOSA trainer as long as it clears the screen enough it is a pass

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/611019/mot-inspection-manual-classes-3-4-5-and-7.pdf

try pdq in exeter, (near sainsburys in pinhoe) he knows his stuff,