To be honest you might be able to use just the built in node test runner (deno and bun also have their own test runners), but IMHO are not as ergonomic as Rust,

To be honest you might be able to use just the built in node test runner (deno and bun also have their own test runners), but IMHO are not as ergonomic as Rust, in Rust you can test private functions in the same file, and that let's you prototype faster, you write a simple function and a test (even when the prototype is not fully functional). In JS land you could do the same I think, but you would need to export all methods that you want to test and they are in other files, and to make things worse you need to setup Typescript to make your IDE more useful and also write less tests, I would argue that in that case vite/vitest will be more helpful because the tests runs with the same config as the bundler, but still, it does not work out of the box as Rust, there might be other languages that have also good ergonomics as Rust in that regard, but none of the languages that I use besides Rust do that.