Match-box trial (4,4)
I believe the answer is:
test case
'trial' is the definition.
(thesaurus)
'match-box' is the wordplay.
'match' becomes 'test' (test match is a kind of match**).
'box' becomes 'case' (I've seen this before).
'test'+'case'='TEST CASE'
(Other definitions for test case that I've seen before include "Court precedent" , "that could set a precedent" , "Possible legal precedent" , "Cassette containing significant lawsuit" , "Legal precedent setter" .)