Well, this is an examination you won’t fail! (7)
I believe the answer is:
medical
This clue could be a double definition.
'well this is an examination you won't' is the first definition.
The definition suggests a singular noun which matches the answer.
'fail' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see an association between them that I can't see?
Can you help me to learn more?
(Other definitions for medical that I've seen before include "Relating to doctors" , "Examination of physical health" , "Thorough health check" , "Relating to doctoring" , "Relating to the art of healing" .)