Weld in section of gun I tested (5)
I believe the answer is:
unite
'weld' is the definition.
(I've seen this in another clue)
'section of gun i tested' is the wordplay.
'section of' indicates the answer is hidden within the clue.
'UNITE' is hidden in the letters of 'gun i tested'.
'in' is the link.
(Other definitions for unite that I've seen before include "Combine - join" , "Join together, merge" , "Couple" , "pool resources" , "Marry" .)