Tester (8)
I believe the answer is:
examiner
'tester' is the definition.
(I know that tester can be written as examiner)
This is the entire clue.
(Other definitions for examiner that I've seen before include "One in charge of test" , "bloke who will make inspection" , "One setting a formal test" , "Assessor" , "Tester of knowledge" .)