IIRC the people who programmed the first auto pilot for a major airliner were required to be on board the first test flight, so I have to think their testing methodology was pretty meticulous.
It wasn't but it increasingly is getting to that point. You take off (with fly by wire adjustments from the computer) from Airport A and tell it to fly to Airport B and it can even automatically land there.
Some airlines do not allow pilots to manually fly above 3k feet, nor allow first mates to land manually[0].
Which then gets you pilots frobbing the autoland selector, not getting the mode right - and now what, if you have zero practice, having scripted yourself out of it? Now you fly the plane into the runway: https://en.wikipedia.org/wiki/Asiana_Airlines_Flight_214
There is a (prevalent) happy path where autopilot and autoland can get you the whole illusion "but the plane flies itself" - but the whole system is built around humans catching and handling all and any exceptions.
