as a rule, we prefix mock-specific properties with m so that they clearly stand out from the original object's properties.

You can have a look at `mock_notification_screen.js` in the system unit tests, it has a generic way of mocking methods. In your case here you'll need to have a specific method because you have to call a callback, but this may help you understand how we do that already.

You can also have a look at the `mock_xmlhttprequest.js` in the homescreen unit tests, this is more ad hoc because XMLHttpRequest is so special, so this can help you too.