Vehicle trial (4,5)
(Other definitions for test drive that I've seen before include "Trial run" , "Assess performance" , "Try out new car" , "Evaluate jeep, say" , "Shot" .)
'vehicle trial' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for road test that I've seen before include "Start ode (anag.)" , "moving trial" , "Examination of vehicle's performance on highway" , "motor trial" , "Try out how something works under realistic conditions" .)