Are they sold? Are they for Boeing’s use exclusively forever? I’m talking about all the hours of testing for the 787 and 747-8. What becomes of these test aircraft? I understand they go through a lot of physics that normal aircraft would not be subjected to on a normal flight.
Does Boeing (or Airbus for that matter) roll a brand new unflown aircraft out of the hanger and deliver to a client or do they give them one that has been test flown for months?
787s: 1-6 were originally planned to be delivered to airline customers. Boeing has since decided to retain 1-3, and 4-6 are going to BBJ customers.
747-8: All being delivered to airline customers.
Airbus tends to hang on to one or a few of the early builds (A320, A340, A380, etc) and use for future testing, Boeing generally delivers them all and buy or lease used frames for various testing.
Aside from the static and fatigue test frames they’re not doing anything you couldn’t do with a production airframe (although you’d have to do a lot of inspections afterward).
The first delivery won’t be a test airframe; it generally takes a while to finish up with them and refurbish them for airline service.