Acceptance Tests...again

I see that this has popped up here and there in previous issue but I am completely lost on how to verify success or failure on my tests.

Some examples seem to indicate you turn on alerts during testing but that slows things down:
// my-acceptence-test.js
import Notify from 'ember-notify';
Notify.testing = true;

I just want to detect if a notify.success() or notify.alert() is called from within the test. I've seen suggestions like "stub out notify.success" and to spy this.notify.alert() but I have no idea how to do that within a test.

Could someone give me a pointing to detect when success() or alert() is called from within an Acceptance test?