The real question is what was this flight for? Transfer from one airline to another after mayor maintenance, in other words to make sure everything was working.
They must be ready for something NOT working or a failure. They were not prepared, qualified or ready for it; that is the bottom line.
Yes they had a failure, but that is exactly what they were looking for. They were not able to identify it.
During this test (and yes, it is a test); the Flight Test Engineer calculates a minimum speed that properly trained and qualified Pilots would NEVER go below because the aircraft will be outside the protection envelope and it will stall.
They put themselves in that situation, should not do that flight without proper training. Learning experience for the rest of us.
Harsh, but true.
They paid the ultimate price for their mistake, God bless them and their families.
G