Ben...what do you think half of game testing is? The whole point of testing is to make sure that the game is stable and reacts to any player input appropriately, and that the player can continue to play the game at any time without having to hard reset the game.
I mean, this is confusing because it's EXTREMELY obvious. I don't think there's a game designer alive who doesn't know this.
It's the same reason we get players to do very weird tests, such as jump in a single spot 5000 times or make bets on whp can break the level's physics and use a tree to jump out of the level bounds.
Furthermore, those solutions...those are not "designer" solutions, they're "player solutions". That's how we would try and justify to the player that the story ingame works, but in terms of the physical gameplay elements, we have special tools such as kill volumes, blocking volumes (invisible walls) or teleports.
It's simply impossible to test the game to get every bug out. A lot of players out there are simply playing to break the game. Others will play the game in ways the designers really didn't intend, and those developers may believe it's the players fault for causing such issues. I personally don't agree with them, but the point is that a lot of game testing is about this one issue. It's not some big secret. It's what we do normally.