Let it stand a new test (4)
I believe the answer is:
stet
'let it stand' is the definition.
(I've seen this before)
'a new test' is the wordplay.
'a new' is an anagram indicator.
'test' anagrammed gives 'STET'.
(Other definitions for stet that I've seen before include "Cancellation of correction" , "Leave as is - don't amend" , "Editing instruction that matter marked for deletion is to be retained" , "Ignore correction" , "Instruction to cancel a deletion" .)