Bug 1007588 -[Cost Control] Implement an IAC mechanism to warn other app...

...lications about sending a SMS for requiring balance or making a SMS top-up
Never, never, never rely on `debugs`, `logs` and informative messages for assertions. These tests are invalid.
So, what to do for truly testing this. First, lets test `_sendBroadcastMessage()`. We need to mock the environment to force the promise used internally to be resolved, then inside the fulfill handler, a simply `assert(true)` is enough and a `done()` call. Inside the `onreject` handler, a pair `assert(false); done();` is enough.

When testing the onreject, we should distinguish two cases: one for the error, and another for timeouts. Assertions on the reason are enough, then `done()`. In the onfulfill handler, install an `assert(false); done();` to catch the incorrect path.

Finally, once this common method is tested, you only need to test the public API by asserting the former method was called with the proper message. That's all.