Swore at journalist covering trial (8)
I believe the answer is:
attested
'swore' is the definition.
(attesting is a kind of swearing)
'at journalist covering trial' is the wordplay.
'journalist' becomes 'ed' (short for editor).
'covering' is an insertion indicator.
'trial' becomes 'test' ('test' can be a synonym of 'trial').
'at'+'ed'='ated'
'ated' placed around 'test' is 'ATTESTED'.
(Other definitions for attested that I've seen before include "Declared that something was true" , "Affirmed to be true" , "Bore witness to" , "Affirmed by oath" , "Provided evidence" .)