He'd test us about protective cover (4,5)
I believe the answer is:
dust sheet
'protective cover' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'he'd test us about' is the wordplay.
'about' is an anagram indicator.
'hed'+'test'+'us'='hedtestus'
'hedtestus' anagrammed gives 'DUST-SHEET'.
Can you help me to learn more?
(Other definitions for dust sheet that I've seen before include "Furniture covering during decoration" , "protection from dirt?" .)