Calm about current opportunity to take test again (5)
I believe the answer is:
resit
'test again' is the definition.
'resit' can be an answer for 'test' (I have seen 'Second test' mean 'resit' so perhaps 'test' could also mean 'resit'). I'm not sure about the 'again' bit.
'calm about current opportunity' is the wordplay.
'calm' becomes 'rest' (I've seen this before).
'about' is an insertion indicator.
'current opportunity' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'rest' enclosing 'i' is 'RESIT'.
'to take' is the link.
Can you help me to learn more?
(Other definitions for resit that I've seen before include "Take examination again" , "second exam" , "Enquiring intrusively (into person's affairs)" , "Exam taken again" , "tested again" .)