Some Mozart is testing for musician? (6)
I believe the answer is:
artist
'musician?' is the definition.
(I've seen this before)
'some mozart is testing' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ARTIST' is hidden within 'mozart is testing'.
'for' is the link.
(Other definitions for artist that I've seen before include "Expert" , "Traits (anag)" , "One engaged in painting" , "One skilled in creative works" , "A painter, sculptor or other creative person" .)