The pilot should have been made aware that his trim was doing a runaway.
This was not a runway at all. It trimmed as designed. Airbus design the system trims for you. This test profile was only meant for a test pilot not a line pilot. That too the pilot suddenly decided to do it at low altitude without any briefing. When NO.3 ADR triggered a stall warning they should have abandoned the exercise. But they dropped speed below that. Even in alternate law if you don't keep back pressure on stick the nose will drop and it will stop trimming.