Yep - totally right. It would involve mocking out the entire browser API in a way that would somehow still follow the same codepaths. That said, it could still

Yep - totally right. It would involve mocking out the entire browser API in a way that would somehow still follow the same codepaths. That said, it could still catch some things. If the web worker errors out, you just completely ignore the errors and just run it anyway. But if it times out, it's (almost) definitely going to time out in the real page too, unless you're waiting for some specific DOM event or something weird.