Even the digital property liberators/internet pirates don’t test their software. I feel like I’m on an island with a small population of test enthusiasts.
Ultimately, what's the point. The tool either works, or it doesn't. Then you patch what doesn't work so it does work.
Heck even the Linux kernel isn't tested.
Unit tests are so management can have a good metric to sell code quality. I don't know any time unit testing has actually benefited shipping faster (which really is the only bottom line those above you care about)
Linux kernel self-tests:
https://kselftest.wiki.kernel.org/
Kselftest is run everyday on several Linux kernel trees on the 0-Day and Linaro Test Farm and other Linux kernel integration test rings.
Most recent update to the source code was yesterday 2021-12-26: