Small getting six in Test (7)
I believe the answer is:
trivial
'small' is the definition.
('trivial' can be a synonym of 'small')
'six in test' is the wordplay.
'six' becomes 'vi' (roman numeral).
'in' indicates putting letters inside.
'test' becomes 'trial' ('trial' can be a synonym of 'test').
'vi' inserted into 'trial' is 'TRIVIAL'.
'getting' acts as a link.
(Other definitions for trivial that I've seen before include "Mundane" , "Rival it, being unimportant" , "Very easy" , "Footling" , "Quite unimportant and paltry" .)