Choice testimonial on page (10)
I believe the answer is:
preference
'choice' is the definition.
(I know that preference is a type of choice)
'testimonial on page' is the wordplay.
'testimonial' becomes 'reference' (reference is a kind of testimonial).
'on' is a charade indicator (letters next to each other).
'page' becomes 'p'.
'reference' after 'p' is 'PREFERENCE'.
(Other definitions for preference that I've seen before include "Favour shown to one person over another" , "First choice" , "Fancy" , "Bent" , "Liking for one thing more than another" .)