Soldiers and supporter entering in test (8)
I believe the answer is:
infantry
'soldiers' is the definition.
(I've seen this before)
'supporter entering in test' is the wordplay.
'supporter' becomes 'fan' (fan is a kind of supporter).
'entering' indicates putting letters inside.
'test' becomes 'try' ('try' can be a synonym of 'test').
'in'+'try'='intry'
'fan' inserted into 'intry' is 'INFANTRY'.
'and' acts as a link.
(Other definitions for infantry that I've seen before include "Men fighting" , "Unmounted fighters" , "Army unit of foot soldiers" , "Foot-soldiers" , "fighting group" .)