In a bad mood (5)
(Other definitions for surly that I've seen before include "Bad-tempered, unfriendly" , "Ill-natured" , "Gruff and grumpy" , "Ill-tempered, unfriendly" , "Morose" .)
'in a bad mood' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for testy that I've seen before include "Ratty" , "Quick to anger" , "Easily annoyed" , "Grumpy" , "snappy" .)