Sort of road test after component has been installed (7)
I believe the answer is:
orbital
'sort of road' is the definition.
(term for a ring road)
'test after component has been installed' is the wordplay.
I cannot quite see how this works, but
'component' could be 'bit' and 'bit' is present in the answer.
'test' could be 'oral' (oral is a type of examination) and 'oral' is located in the remaining letters.
No letters remain.
This explanation may well be incorrect...
(Other definitions for orbital that I've seen before include "Following a path around a heavenly body" , "Like a sort of road" , "Going round the world" , "Going round - the M25?" , "going round the city" .)