[Prophet in the wilderness]

You might be right about the 777 , but, at least one of the new program or new airplane design is sacrificed ( take one for the team ) is tested for fatigue and broken into pieces.
I do know, at least 2 of the 747's never went into regular service.
I do have a great book on the history of the 747 ... it's called ( The Boeing 747 - design and development since 1969 ( really, since 1966 ) by Guy Norris and Mark Wagner.

[Paleo Conservative]

You might be right about the 777 , but, at least one of the new program or new airplane design is sacrificed ( take one for the team ) is tested for fatigue and broken into pieces.

I don't think the ones used for fatigue tests ever were fitted out with a flight deck or interior. There's one test where they measure how much force it takes to break the wings, and another one where they put the fuselage in a water tank and simulate tens or hundreds of thousands of pressurization cycles till the hull fails due to metal fatigue.

[Central Scrutiniser]

The first 777 ever built is still flying for its original customer, United Airlines.