A practice exam delivered orally: that's crazy (4)
I believe the answer is:
amok
'crazy' is the definition.
(I've seen this before)
'a practice exam delivered orally' is the wordplay.
'practice exam' becomes 'mock'.
'delivered orally' indicates a 'sounds like' (homophone) clue.
'a'+'mock'='amock'
'amock' sounds like 'AMOK'.
'that's' is the link.
(Other definitions for amok that I've seen before include "Running wild" , "going wild" , "Going mad" , "crazy" , "(Run) in frenzied state" .)