Single test covering end of term is better (7)
I believe the answer is:
improve
'better' is the definition.
('improve' can be a synonym of 'better')
'single test covering end of term' is the wordplay.
'single' becomes 'i' (one).
'test' becomes 'prove' ('prove' can be a synonym of 'test'**).
'covering' indicates putting letters inside.
'end of' suggests the final letters.
The final letter of 'term' is 'm'.
'i'+'prove'='iprove'
'iprove' placed around 'm' is 'IMPROVE'.
'is' acts as a link.
(Other definitions for improve that I've seen before include "Change for the better" , "Ameliorate" , "Train" , "pick up" , "reform" .)