Unusual tests on a hat (7)
I believe the answer is:
stetson
'a hat' is the definition.
(Stetson is an example)
'unusual tests on' is the wordplay.
'unusual' indicates an anagram.
'tests' with letters rearranged gives 'stets'.
'stets'+'on'='STETSON'
(Other definitions for stetson that I've seen before include "Hat with broad brim and high crown" , "No tests (anag.)" , "capital item" , "Ten-gallon hat" , "Capital investment" .)