Tested for counterfeit currency? Not this one! (7)
I believe the answer is:
bitcoin
'not this one' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'tested for counterfeit currency?' is the wordplay.
'tested for counterfeit' becomes 'bit' (I can't explain this - if you can you should give a lot more credence to this answer).
'currency?' becomes 'coin' (coin is a kind of currency).
'bit'+'coin'='BITCOIN'
(Other definitions for bitcoin that I've seen before include "Digital currency" , "new money" .)