Test end of zip on dress (5)
I believe the answer is:
probe
'test' is the definition.
(probe can mean to test or experiment)
'end of zip on dress' is the wordplay.
'end of' suggests the final letters.
'on' is a charade indicator (letters next to each other).
'dress' becomes 'robe' (robing is a kind of dressing).
The last letter of 'zip' is 'p'.
'p'+'robe'='PROBE'
(Other definitions for probe that I've seen before include "Investigate closely" , "Explore, examine" , "Question or examine thoroughly" , "sound" , "Intrusive device" .)