Test for car, one following distinctive pattern (5)
I believe the answer is:
motif
'distinctive pattern' is the definition.
'test for car one following' is the wordplay.
'test for car' becomes 'mot' (Ministry of Transport test).
'one' becomes 'i' (Roman numeral).
'following' becomes 'f' (used when citing page numbers etc).
'mot'+'i'+'f'='MOTIF'
(Other definitions for motif that I've seen before include "Theme in a work of art" , "Distinctive theme in art" , "Theme, perhaps musical" , "Repeated theme" , "Theme or melody" .)