Taxi tests and high power engine runs prior to delivery are done by technicians at Airbus, even for A380s. The people doing this are at all times alert with the 'PF' with a hand on the throttle and ready to respond while the 'PNF' is running checklists to verify everything they are testing. A widebody gets quite agitated when in the testing stand on full throttle. Especially after the A346 incident in TLS all the testing crews absolutely know what to do if certain things happen, they are trained for it. A regular 'pilot' wouldn't know more or less.