Provides evidence that is found in conditions following trial (9)
I believe the answer is:
testifies
'provides evidence that is found in conditions following trial' is the definition.
I can't judge whether this definition defines the answer.
'provides evidence that is found in conditions following' is the wordplay.
'provides evidence' becomes 'test' (I can't explain this - if you can you should give a lot more credence to this answer).
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'found in' means one lot of letters goes inside another.
'conditions' becomes 'ifs' (I've seen this before).
'following' is a charade indicator (letters next to each other).
'ie' inserted within 'ifs' is 'ifies'.
'test'+'ifies'='TESTIFIES'
Can you help me to learn more?
(Another definition for testifies that I've seen is " Gives evidence".)