It seems so obvious to me that your typical engineer, who spent hours / days / whatever working on a feature, is never going to test the edge cases that they didn’t conceive of during implementation. And if they didn’t think of it, I bet they’re not handling it correctly.

Sometimes that’ll get caught in code review, if your reviewer is thinking about the implementation.

I’ve worked in payroll and finance software. I don’t like it when users are the ones finding the bugs for us.