I don't think there has been a fast jet test pilot qualified in over 30 years who hadn't been an operational FJ pilot, and doubt that there will be again. (Okay, specialist transport or training aeroplane TPs will fly FJ occasionally, but I've never met one for whom it became their main job.)
Is there a difference (either morally or in terms of personal safety) between flying a front-line FJ and working on the testing and development of one? About 8 years ago when a false-start was happening on GW-II, I was earning my living sat in the back of a 2-seat Jaguar as FTE evaluating the corners of the envelope for high angle / high Mach ground attack dives - I don't recall myself or the RAF Officer (and GW I veteran) in the front seat ever commenting that we were glad to be safely at Boscombe Down instead of out in the desert somewhere.
G