Subject to a fitting test (3,2)
I believe the answer is:
try on
'test' is the definition.
(try-on is a kind of test)
'subject to a fitting' is the wordplay.
I cannot quite see how this works, but
'subject to' could be 'on' (I've seen this in other clues) and 'on' is located in the answer.
The remaining letters 'try' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for try on that I've seen before include "Test a garment for fit" , "audacious imposition" , "Check the fit of (a garment)" , "Test a garment's size and look" , "attempt to sneak an advantage?" .)