Test round part is going round (7)
I believe the answer is:
orbital
'going round' is the definition.
(I've seen this before)
'test round part' is the wordplay.
'test' becomes 'oral' (oral is a type of examination).
'round' indicates putting letters inside.
'part' becomes 'bit' (bit is a kind of part).
'oral' going around 'bit' is 'ORBITAL'.
'is' is the link.
(Other definitions for orbital that I've seen before include "Like a ring road" , "Revolutionary" , "Descriptive of the M25" , "Boil tar (anag)" , "Relating to planet's motion" .)