[solid_fuel]

No I'm not missing anything. The existing specifications and tests provide a huge validation surface to work against for this kind of migration - they're the foundational pieces of the control loop. Without those two things, this kind of rewrite would not be possible.

We have known for decades that the hard part in programming isn't programming, it's making sure you have the right target! Bad designs and bad specifications have caused more bugs and broken software than anything else, and the time taken to develop the testing and validation suites (that is - the javascript spec tests) this rewrite used must be considered part of the engineering effort.

> and btw, if it can write code, it can write tests and test suite

You must be very early in your career. Again, the hard part is not writing the test, it's knowing which tests to write.