[lolinder]

If when you hear "there's a lot of overlap between type checking and unit testing" your first thought is of Java's type system then I can definitely see why you'd be concerned.

Java's type system at the time you're referring to was extremely limited compared to Rust's ML-like type system or even TypeScript. It didn't need to be said back then that the type system wouldn't catch everything because Java's couldn't even catch null pointer exceptions, much less encode error states as algebraic data types or provide zero-overhead newtypes.

I agree that types can't catch everything, but a modern type system like Rust's can be used to prevent many more classes of bugs than just "oops, that was supposed to be an int not a float", and that's all OP is saying: if you're using your type system to its fullest you need many fewer tests than you do in a dynamic language.