Authorise secretary to return test (7)
I believe the answer is:
approve
'authorise' is the definition.
(approving is a kind of authorising)
'secretary to return test' is the wordplay.
'secretary' becomes 'pa' (I've seen this in other clues).
'to return' shows that the letters should be reversed in order.
'test' becomes 'prove' ('prove' can be a synonym of 'test'**).
'pa' reversed gives 'ap'.
'ap'+'prove'='APPROVE'
(Other definitions for approve that I've seen before include "Confirm" , "Give the green light" , "Sanction, authorise" , "OK" , "Commend, endorse" .)