Means of abandonment, including drills on the ground, are always part of the work-up for a stalling trial. Yes, the prototype Concorde had an escape chute, I've seen photos of it being tested with dummies.
Stall tests are always (at least initially) done high enough to allow safe abandonment, and a mandatory abandonment height will be part of the sortie brief. (I recall doing Tucano spinning trials, the brief was that at x,000ft I would eject from the rear to try and recover it for the chap in the front to bring the a/c back - thankfully I never had to).
G