the.com/test pilot

means A pilot who flies new or modified aircraft to find out, deliberately and methodically, what they can do and where they break.

from Straightforward compound coinage from 'test' (Latin testum, an earthen pot used in assaying metals — the sense drifted from 'trial by fire' to 'trial' generally) plus 'pilot' (via French pilote, probably from Greek pēdon, 'steering oar'). The job and the job title emerged together in the early 20th century, as powered flight matured and manufacturers needed someone willing to find a new aircraft's limits before customers or the military did.