Testify with very pained expression? (5)
I believe the answer is:
vouch
'testify' is the definition.
(I know that vouch is a more specific form of the action testify)
'with very pained expression?' is the wordplay.
'with' says to put letters next to each other.
'very' becomes 'v' (abbreviation).
'pained expression?' becomes 'ouch' (I've seen this in another clue).
'v' next to 'ouch' is 'VOUCH'.
(Other definitions for vouch that I've seen before include "Be surety (for)" , "warrant" , "Declare support" , "Testify" , "Give personal assurance; guarantee" .)