Test code written by a human counts as "tested by a human". Also, most code is literally tested (manually) by humans in addition to automated tests. You are being pointlessly pedantic.

Bun has a test suite of tens of thousands of tests. For purely non-functional changes, like refactors or rewrites (e.g. a Rust rewrite) I rely primarily on test suites, not manual testing, in order to ensure that nothing regressed. I mean, sure, I am going to poke around, too, but the test suite is the encoding of thousands of obscure bugs and issues over years. There is no way my manual testing will be able to cover the same ground.