Yeah, that whole suite of tests that you don't have to write yourself (or, more likely, you were never going to write, if you had to do it yourself...) that runs automatically every time called a compiler.

That's misleading. You don't write tests to check types. You write the same tests you would with a typed language. There is no extra work.

A by product of testing your logic is that it will fail if there is a type cast problem.