Indeed, as these are error classes unit tests aren't even very good at. It can't be repeated enough: Types are universal quantifiers, tests are existential qua

Indeed, as these are error classes unit tests aren't even very good at. It can't be repeated enough: Types are universal quantifiers, tests are existential quantifiers, you'll realistically never get even close to the guarantees of a type system with tests alone. If your unit tests are on a level with your static type system, you have basically rebuilt the static type system in your unit tests. (And pitting unit tests against a static type system is a false dichotomy, it's good to have both.)