I'm not the person you're replying to, but I don't think that's what they're saying. When I write Python, I'm paranoid that someone will pass a string instead

I'm not the person you're replying to, but I don't think that's what they're saying. When I write Python, I'm paranoid that someone will pass a string instead of an int to my function. Or that when I for-loop over my tuple of strings, I'll accidentally iterate over the characters in the (single) string of my (1-)tuple, instead of the many strings in a n-tuple (with n>1). So I write unit tests to cover these specific cases. When I'm writing Java or Go, I write all the other tests, but not those ones. Because the type checker would catch those problems for me.