In test, target splits (6)
I believe the answer is:
trendy
'in' is the definition.
('in' can mean trendy or fashionable)
'test target splits' is the wordplay.
'test' becomes 'try' (synonyms).
'target' becomes 'end' (end can mean one's purpose or goal).
'splits' is an insertion indicator (inserted letters split open the word).
'try' enclosing 'end' is 'TRENDY'.
(Other definitions for trendy that I've seen before include "Cool" , "Chic (colloq.)" , "With it, a la mode" , "Up-to-date with the latest fad" , "In accordance with the latest fad" .)