Bear witness at trial (6)

I believe the answer is:

attest

'bear witness' is the definition.
(I know that bear witness can be written as attest)

'at trial' is the wordplay.
'trial' becomes 'test' (synonyms).
'at'+'test'='ATTEST'

(Other definitions for attest that I've seen before include "Confirm to be true" , "Adjure" , "Demonstrate" , "Provide firm evidence" , "Vouch for" .)

I've seen this clue in the Sydney Morning Herald.

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