Some into testing betting system (4)
I believe the answer is:
tote
'betting system' is the definition.
(I've seen this before)
'some into testing' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'TOTE' is hidden in the letters of 'into testing'.
(Other definitions for tote that I've seen before include "record of stakeholders' investments" , "move" , "convey" , "Bear" , "Large bag" .)