Threesome employed as computer technicians in test (7)
I believe the answer is:
trinity
'threesome' is the definition.
('trinity' can be a synonym of 'threesome')
'technicians in test' is the wordplay.
'technicians' becomes 'init' (I am not sure about this - if you are sure you should believe this answer much more).
'in' means one lot of letters goes inside another.
'test' becomes 'try' ('try' can be a synonym of 'test').
'init' inserted inside 'try' is 'TRINITY'.
'employed as computer' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for trinity that I've seen before include "Group of three considered as one" , "Father, Son and Holy Spirit" , "A group of three people" , "Term" , "Cambridge college founded by Henry VIII" .)