If you have an E2E test that tests the button behavior thoroughly (i.e. not just showing it, but the fact that, when it's clicked, the app state changes accordingly), then you have a test showing that "code that put it there worked".
``` function setButtonState() { const res = this.fetchSomeResult(); // returns an unfulfilled promise if (res) { return true; }
return false;as a unit test would quickly fail when you want it to. An E2E test would pass, but for the wrong reasons. This has nothing to do with app state, and everything to do with not being scientific, and testing all sorts of variable things at once just because, "that's what the user sees".
If there's no such observable behavior, then why does it matter?
The appeal to "being scientific" doesn't make much sense to me, either. But if you really want to go there, being scientific is all about app state since that's literally all there is to the app.