Tricky criminal gets to carry can (7)
I believe the answer is:
testing
'tricky' is the definition.
'criminal gets to carry can' is the wordplay.
'criminal' indicates an anagram.
'to carry' indicates putting letters inside.
'can' becomes 'tin' (synonyms).
'gets' anagrammed gives 'tesg'.
'tesg' enclosing 'tin' is 'TESTING'.
(Other definitions for testing that I've seen before include "tiresome" , "... conducting exam" , "stressful" , "Subjecting to 15 ac" , "Trying out" .)