Ordeal on last test drive (5,3)
I believe the answer is:
trial run
'test drive' is the definition.
(I've seen this before)
'ordeal on last' is the wordplay.
'ordeal' becomes 'trial' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'last' becomes 'run' (running is a kind of lasting).
'trial'+'run'='TRIAL RUN'
(Other definitions for trial run that I've seen before include "Introductory test" , "Preliminary evaluation like test trot" , "Practice attempt" , "A test for a car" , "Test procedure - on the trot?" .)