I disagree with Eckel on this one. The reality is that most of your tests end up being a matter of testing the things that the compiler would have done for you

I disagree with Eckel on this one. The reality is that most of your tests end up being a matter of testing the things that the compiler would have done for you for free and that's the kind of thing that computers should be doing, not people. Also, tests don't have 100% coverage whereas the compiler will enforce type correctness everywhere. I've spent days hunting down bugs in Javascript which would have been automatically caught by a type checking compiler. That's just a waste of my time, as is reproducing all the type checking that the compiler would have done in the first place.