Easily irritated (9)
'easily irritated' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for testy that I've seen before include "Showing irritation" , "Captious" , "bad temper" , "Easily irritated" , "Bad-tempered" .)
(Other definitions for sensitive that I've seen before include "Delicate" , "Emotional or perceptive" , "Reacting to external stimuli" , "Easily offended or upset" , "Controversial" .)