Tape in difficult test case (8)
I believe the answer is:
cassette
'tape' is the definition.
(I know that tape can be written as cassette)
'difficult test case' is the wordplay.
'difficult' indicates an anagram.
'test'+'case'='testcase'
'testcase' with letters rearranged gives 'CASSETTE'.
'in' acts as a link.
(Other definitions for cassette that I've seen before include "Small sealed case of magnetic tape" , "Music tape" , "Box of recordings" , "Recording medium" , "It may contain film" .)