Test explosive device after returning fire (7)
I believe the answer is:
examine
'test' is the definition.
('examine' can be a synonym of 'test')
'explosive device after returning fire' is the wordplay.
'explosive device' becomes 'mine' (mine is a kind of explosive device).
'after' is a charade indicator (letters next to each other).
'returning' says the letters should be written backwards.
'fire' becomes 'axe' (I've seen this before**).
'axe' backwards is 'exa'.
'mine' after 'exa' is 'EXAMINE'.
(Other definitions for examine that I've seen before include "Inspect; question in court" , "Question (a witness)" , "Look closely at < test" , "Inspect carefully" , "Inspect , test" .)