Restore Test ground (4)
I believe the answer is:
stet
'restore' is the definition.
(I've seen this before)
'test ground' is the wordplay.
'ground' is an anagram indicator (grind the letters ).
'test' with letters rearranged gives 'STET'.
(Other definitions for stet that I've seen before include "Proofreader's mark that the original text should be kept" , "Mark on page to restore a deletion" , "Instruction to cancel a deletion" , "Let it remain (printing)" , "Don't alter, let spelling stand" .)