Roll introduced in test hearing (8)
I believe the answer is:
tribunal
'hearing' is the definition.
(I've seen this before)
'roll introduced in test' is the wordplay.
'roll' becomes 'bun' (synonyms).
'introduced in' is an insertion indicator.
'test' becomes 'trial' (synonyms).
'bun' going within 'trial' is 'TRIBUNAL'.
(Other definitions for tribunal that I've seen before include "Court of arbitration - unlit bar (anag)" , "Special investigation team constituted in brutal mode" , "Official board" , "case" , "Judgement seat" .)