Gents... The original query is for
'Post Maintenance'.
EASA Part 145 requirements are as follows:
Post Maintenance test flight that you refer to is called a "
Maintenance Check Flight" (Or Category 4 as per the recent EASA NPA).
An appropriately type rated B1, B2 or C licensed engineer responsible for the release to service of an aircraft from either Base or Line maintenance is solely responsible for deciding if a 'Maintenance Check Flight' is required or not.
The licensed Engineer must stipulate and brief precisely how, why what and where the test is to be conducted. The above CAA hand book provides excellent general guidance to the Certification Engineer and Pilot for this but the certification engineer is the one qualified and responsible for any technical requirements / procedures and detail of that
specific test accordingly.
Under Part 145 requirements this detail is now transferred to the 'Flight Test' box on the 'Tech Log'. He / she will normally act as Flight Test Engineer and supervise the check flight to his / her satisfaction. He or she may at their discretion brief and delegate the test duties to the pilot and rely upon the pilots report at the post Maintenance Check Flight debrief.
There is currently no specific qualification or requirements laid down for the flight test engineer or pilot. However, EASA seem to be addressing this and have produced a NPA of which is currently subject to consultation.
http://hub.easa.europa.eu/crt/docs/viewnpa/id_53