Severe test — exam without notes (6)
I believe the answer is:
ordeal
'severe test' is the definition.
(I've seen this before)
'exam without notes' is the wordplay.
'exam' becomes 'oral' (oral exam is a kind of exam).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'notes' becomes 'de' (**).
'oral' going around 'de' is 'ORDEAL'.
(Other definitions for ordeal that I've seen before include "trying affair" , "Trial; nightmare" , "Loader (anag.)" , "A test of endurance or or difficult experience" , "Horrific experience" .)