Emphatically declare as oppressive to introduce a final test (10)
I believe the answer is:
asseverate
'emphatically declare' is the definition.
'asseverate' can be an answer for 'declare' (I've seen this before). I am not certain of the 'emphatically' bit.
'as oppressive to introduce a final test' is the wordplay.
I cannot really understand how this works, but
'as' is within the answer.
'a' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for asseverate that I've seen before include "Claim" , "Swear" , "Solemnly say" , "State categorically" , "Solemnly declare" .)