I'm a mech E in the medical field. We're consistently understaffed. If I validate an Excel worksheet in Excel '08 or a Python program in 3.5 with a specific version of NumPy, we're probably sticking with those versions for a while. Every time I bring up re-validating with the latest version, keeping one old system running the old software requires fewer resources than me or a colleague re-validating.

My whole department is stuck on one version of Python because that was the most recent version when I had an emergency project and developed a data analysis algorithm. We validated it, then as new members were added to my team, they needed a copy, so we had to keep using it. I'll probably re-validate it to the next Python release. It's not only unit tests, or we could automate validation. Unit tests are a tiny part of validating software for making medical decisions. And software that directly runs a medical device (like firmware on an insulin pump) is an order of magnitude more rigorous than what I do.

Side note: there are people who somehow root their insulin pumps and run algorithms on them. There's a group that can get a PID control loop on an insulin pump that has a more simple control scheme on it (because that's how the FDA approved it). The company has been trying to get approval to use PID control in the US for years.