Part of a computer testing an organised campaign (4,5)
I believe the answer is:
hard drive
'part' is the definition.
(I know that hard drive is a type of computer hardware)
'organised campaign' is the wordplay.
'organised' becomes 'hard' (I can't explain this - if you can you should give a lot more credence to this answer).
'campaign' becomes 'drive' (drive can mean a campaign or initiative).
'hard'+'drive'='HARD DRIVE'
'of a computer testing an' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for hard drive that I've seen before include "Computer component" , "storage facility" .)