Test gold with aluminium (4)
I believe the answer is:
oral
'test' is the definition.
(oral is a type of examination)
'gold with aluminium' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'with' means one lot of letters go next to another.
'aluminium' becomes 'al' (Al is the chemical symbol for aluminium).
'or'+'al'='ORAL'
(Other definitions for oral that I've seen before include "Type of examination" , "Type of exam" , "Spoken exam" , "Kind of exam" , "Spoken test" .)