What edge cases in tests do you see other devs often missing?

I try to be thorough in writing tests for my code. I often walk away from a test with a nagging feeling that I've missed some important edge cases that should be asserted. My learning on the subject is usually seeing something in someone else's tests that I hadn't thought of. There's not a lot of good blog articles on the subject -- something like "here's what you should test for in these different scenarios", at least that I've been able to find.What am I probably often missing? What assertions do you see other devs missing that they should have tested, for different common scenarios?

Submitted January 08, 2018 at 12:40PM by calligraphic-io