How many tests do other JS runtimes like V8 have? ~400 tests sounds reasonable for a single data structure, but orders of magnitude off for a language runtime.

MicroQuickJS has 7, kind of: https://github.com/bellard/mquickjs/tree/main/tests

Though if you look in those files some of them run a ton of test functions and assertions.

My new Python library executes copies of the tests from that mquickjs repo - but those only count as 7 of the 400+ other tests.