The `fail` part is missing. As said in previous review, it would be better if we check that only the callback that are supposed to be called are actually called. So, in this example we expect no `onInteractive` neither `onComplete` to be executed. Therefore we should have:
```js
  handleReadyState(url, 'start', {
    onLoading: tab => {
      assert.pass('PageMod is attached while document is loading');
      if (++count === 3)
        tab.close(done);
    },
    onInteractive: () => assert.fail('onInteractive should not be called with "start".'),
    onComplete: () => assert.fail('onComplete should not be called with "start".')
  });