When you are in the air there are no FAA inspectors looking over your back or breathing down your neck. Boeing can monitor things that go bad and then report back to management but not the general public. Its called no you see the major problem - no you don't. Boeing tells FAA and general public test flight was uneventful, but Boeing pilots and electrical engineers (on test flight) know different and have sworn their alliance to BA management and their weekly paychecks.
Always best to go to 20,000 ft up in the air to do your bogus tests, thus making sure the the FAA is far, far away when the real problems surface. Problems like the whole electrical system within the Dreamliner might be defective.