That's not the same thing, I think he's referring to the fact that in Rust you can keep unit tests and code in the same file, and strip them away at build time.

That's not the same thing, I think he's referring to the fact that in Rust you can keep unit tests and code in the same file, and strip them away at build time. That's not a thing in the js world (and most other languages), where tests must be in a different file and you are forced to export functions to test them, even if you wanted to keep them private in that file.