Someone who tests old flame, a collier (8)
I believe the answer is:
examiner
'someone who tests' is the definition.
'old flame a collier' is the wordplay.
'old flame' becomes 'ex' (I've seen this in other clues).
'collier' becomes 'miner' (I've seen this before).
'ex'+'a'+'miner'='EXAMINER'
(Other definitions for examiner that I've seen before include "Meaner XI (anag)" , "One administering test" , "Tester of knowledge" , "judge" , "Who judges" .)