Took the test again after returning a shocker (5)
I believe the answer is:
taser
'a shocker' is the definition.
(something which gives electric shocks)
'took the test again after returning' is the wordplay.
'took the test' becomes 'tas' (I can't explain this - if you can you should believe this answer much more).
'again' becomes 're' (prefix meaning 'again').
'after returning' says the letters should be written backwards.
're' back-to-front is 'er'.
'tas'+'er'='TASER'
Can you help me to learn more?
(Other definitions for taser that I've seen before include "The weapon delivers a temporary paralysing electric shock" , "Device used to stun someone temporarily" , "A temporary stunner?" , "Shocking device used by the police?" , "PC kit" .)