Re: "US, Canada finally ground 737 Max jets..."
Standard software testing procedure (at least when I was in college) was to feed out of bounds data into a program and examine the results. We were also expected to consider how such data might arise in real world usage and code suitable error handling procedures. It's pretty damned clear that the systems in question were never properly subjected to GIGO testing.
No mission critical system should ever be released for production without it first being subjected to comprehensive tests intended to break it.