Testing centre, party or a politician (10)
I believe the answer is:
laboratory
'testing centre' is the definition.
(where scientific tests are done)
'party or a politician' is the wordplay.
'party' becomes 'lab' (abbreviation for Labour).
'politician' becomes 'tory' (term for a Conservative Party politician).
'lab'+'or'+'a'+'tory'='LABORATORY'
(Other definitions for laboratory that I've seen before include "Experimental area" , "workplace" , "Where litmus paper could be" , "Where researchers work" , "Place of scientific research" .)