The unequivocal answer is yes you can wear your sunglasses during your driving test.
If the sun glare off the road is poor, because it is wet and reflecting the sunlight, the sun is low in the sky or it is just a very bright sunny day and it is going to affect your visibility, then wear sunglasses. When it is really bright the road can just look white, which makes it hard to distinguish road markings and spot any hazards. Where appropriate our driving instructors encourage clients to bring sunglasses to their lessons so they get used to driving while wearing them. If you wear prescription lenses then we would recommend asking the optician for a pair of prescription sunglasses.