[paavohtl]

A formal specification would be basically useless, if nothing guarantees that the reference implementation actually follows it. Sharing & contributing to the same test suite is a much more practical approach.

[quickthrower2]

As a smoke you can swap it in for a lot of the npm ecosystem and run the tests of those projects on the compiled code.

[andreypopp]

Specification isn't being followed is of course useless. But yeah, tests are definitely useless and in the absence of the spec is the only sane way to approach such rewrite.