Test in Oval with area separating sides (4)
I believe the answer is:
oral
'test' is the definition.
(oral is a type of examination)
'oval with area separating sides' is the wordplay.
'oval' becomes 'O'.
'with' is a charade indicator (letters next to each other).
'area' becomes 'a' (maths abbreviation).
'separating' indicates putting letters inside.
'sides' becomes 'RL' (abbreviations for right and left).
'a' put within 'rl' is 'ral'.
'o'+'ral'='ORAL'
'in' acts as a link.
(Other definitions for oral that I've seen before include "Type of exam" , "Via the mouth" , "By word of mouth, say exam" , "'Spoken, not written (4)'" , "Related to the mouth" .)