Let it stand a different test (4)
I believe the answer is:
stet
'let it stand' is the definition.
(I've seen this before)
'a different test' is the wordplay.
'a different' indicates an anagram.
'test' is an anagram of 'STET'.
(Other definitions for stet that I've seen before include "Printing instruction: "Let it stand"" , "cancel amendment" , "indicates second thoughts are not always better" , "Printer's annotation - let it stand" , "Retainer" .)