I wonder if there is a Boeing article somewhere on their recent effort that might explain the process. The Gulfstream test pilots out of SAV also seem to do a little drawing at times but I don't know if it's generated in advance.
It's been a long time since I've done a maintenance test flight but the actual filed flight plan was simple and we requested altitudes and headings once airborne.
Here is a piece on the recent 787 track during an ETOPS test flight:
https://www.flightradar24.com/blog/b...ng-etops-test/