Test fish over year (3,3)
I believe the answer is:
try out
'test' is the definition.
('try out' can be a synonym of 'test')
'fish over year' is the wordplay.
'fish' becomes 'trout' (trout is a kind of fish**).
'over' means one lot of letters goes inside another.
'year' becomes 'y'.
'trout' placed around 'y' is 'TRY-OUT'.
(Other definitions for try out that I've seen before include "Put to experimental use" , "Taste" , "Test and evaluate" , "Sample" .)