What I imagined here is something like:
```javascript
var expectedTextContent = _('callDurationMinutes', duration);
fakeDurationChildNode.textContent = expectedTextContent;
MockNavigatorMozTelephony.conferenceGroup.state = '';
MockNavigatorMozTelephony.mTriggerGroupStateChange();
assert.equal(fakeTotalDurationChildNode.textContent, expectedTextContent);
```