[viraptor]

Usually it's two groups: 1. regular usage as seen now or expected in the future, 2. exercising all existing error paths. I'm pretty confident that it's both a reasonable coverage and that there are going to be some missed patterns. It's "good enough"

[gashaw]

What about cases where "good enough" is not enough? code that handles money comes to mind.

[viraptor]

When you need to handle money correctly, you have more budget for testing to do this correctly ;-)

[gus_massa]

Also, after a bug is fixed add the reproduction case to prevent regressions.