I'm put to the test and made better (8)
I believe the answer is:
improved
'made better' is the definition.
('improve' can be a synonym of 'make better')
'i'm put to the test' is the wordplay.
'put to the test' becomes 'proved' (I've seen this in another clue).
'im'+'proved'='IMPROVED'
'and' acts as a link.
(Other definitions for improved that I've seen before include "Became better" , "Grew or made better" , "Made or got better" , "Made progress" , "Made better in quality" .)