Something from the baker a fool is about to test (6)
I believe the answer is:
pastry
'something from the baker' is the definition.
'a fool is about to test' is the wordplay.
'a fool' becomes 'sap' (synonyms).
'is about' says the letters should be written backwards.
'to test' becomes 'try' (synonyms).
'sap' back-to-front is 'pas'.
'pas'+'try'='PASTRY'
(Other definitions for pastry that I've seen before include "croissant?" , "Dough for baking" , "choux, perhaps" , "Foodstuff flattened with a rolling pin" , "'Dough of flour, fat and water (6)'" .)