If you have a windscreen, the lack of washers and wipers would certainly be a construction and use offence.
Aeroscreeens are exempt - because you don't have to look through them to see where you are going.
Certainly the condition of the wiper blades if fitted is a testable item, but not sure about if they are not there at all whether it would be a fail. I could ask an MOT tester, but he'd only tell me off for being silly. And since I'll never do it, pointless.
It is true construction and use violations are rarely enforced, and poorly understood but expect to have the book thrown at you if you have an accident. Police vehicle examiners do usually know!
