The problem with interactive computer systems with both synchronous and async interactions is that any amount of testing does not make sure they always work. You have to get it right by design, not by testing. In earlier days there were computer languages like ADA that supported (not guaranteed) a proper design with special system calls like the "rendezvous" and "resource locking". Such a design never works in a hurry and is extremly difficult to fix without creating more problems. This is the sort of a task that a clever single software engineer is better suited to solve than a hundred programmers working for a few dollars (or more).
I had a laugh last summer when Muilenburg boasted he could change the single sensor FCC into a communicating and comparing dual channel system in a matter of weeks. The laugh is still echoing.
Last edited by clearedtocross; 20th Jan 2020 at 17:35.