Test returns in regular order (4)
I believe the answer is:
oral
'test' is the definition.
(oral is a type of examination)
'returns in regular order' is the wordplay.
'returns' shows that the letters should be reversed in order.
'in' indicates a hidden word.
'laro' is hidden within 'regular order'.
'laro' reversed gives 'ORAL'.
(Other definitions for oral that I've seen before include "Relating to the mouth - exam" , "Mouth-related" , "Viva voce" , "By word of mouth (4)" , "Spoken - examination" .)