Capt.K, I think you will find that each company will have certain approved pilots for airtesting an aircraft after maintenance,puchase,pre-delivery,etc. Each `CAA` will have also approved the company`s choice,and to what level of testing they are approved,ie just a radio/nav. installation,or a major rebuild after possible damage.
My own experience is military tp,then later CAA civil approval....
I`m sure in EASA-land there is documentation that will give all the information ......