In case, in short, do this? (7)
I believe the answer is:
testify
'do this?' is the definition.
The definition suggests a singular noun but the answer is not.
'in case in short' is the wordplay.
'in case' becomes 'if' (if means in a particular case).
'in' indicates putting letters inside.
'short' becomes 'testy' (both can mean angry).
'if' put into 'testy' is 'TESTIFY'.
Can you help me to learn more?
(Other definitions for testify that I've seen before include "sworn" , "Bear witness in court" , "take the stand" , "Affirm (on oath)" , "Give evidence in court" .)