Milan,
This subject comes up at least every couple of years. The previous threads are referenced in the links at the top of this forum but, alas, have been deleted.
Having worked in Commercial Flight Test for over 25 years, I would recommend the Industry Engineering route. No matter how much Engineering education or training you can get, there is no substitute for actually working in a Flight Test Department. This is because it requires a particular mind set to carry out aircraft testing safely and economically - a different mind set even to that of an Aircraft Design Organization IMHO.
To follow this route, first apply as an engineer to a company with an active flight test program - Airbus in your case, Gulfstream in the USA. You will find that most engineers in Flight Test are, in fact, a vital part of the team and, depending to a certain extent on the company philosophy, may well be carrying out some or all of the duties of a FTE including flying on test aircraft.