Appear in court, say, if brought in quarrelsome (7)
I believe the answer is:
testify
'appear in court' is the definition.
I can't judge whether this definition defines the answer.
'if brought in quarrelsome' is the wordplay.
'brought in' means one lot of letters goes inside another.
'quarrelsome' becomes 'testy' (I can't justify this - if you can you should believe this answer much more).
'if' going within 'testy' is 'TESTIFY'.
'say' is the link.
Can you help me to learn more?
(Other definitions for testify that I've seen before include "take the stand" , "Affirm (on oath)" , "sworn" , "Give evidence in court" , "Bear witness in court" .)