consider for example Airbus, AWH, Diamond, BNG
Not JAR25, but just out of interest, most of the guys who do the production testing at Diamond just hold a PPL. They're on the whole engineers and technicians who have designed and built the aircraft and are paid as such, rather than as pilots, so no need even for a CPL. There are, of course, TPs doing the development flying who have been through TP training.