Firebase messaging frame

[mr-kew]

Just the general frame for firebase messaging library. See #467.

• It allows access to the native libraries
• Firebase messaging APIs will be usable with this library without need for them to be imported & managed separately
• Tests are not implemented because android version of library doesn't provide getInstance(app: FirebaseApp) which would probably be needed to inject the testing FirebaseApp, also firebase-functions does not implement tests as well
• JVM version does not seem to exist, so I marked it with TODO, taking inspiration from firebase-crashlytics

[nbransby]

There are a few more places to add firebase messaging (for example the readme), if you search everywhere for one of the existing modules to make sure you have added messaging to all of the required places.

For the tests you can just add one test case asserting Firebase.messaging doesn't return null or throw an exception.

[mr-kew]

@nbransby Okay, I did add the messaging to all the places I could find. I hope I did not miss any.

As for the tests, I don't really understand what you mean. I dont have access to Firebase.messaging(app: FirebaseApp) function as the platforms don't have it. So I can just do a simple test like this:

@Test
fun testConstruction() {
    assertNotNull(Firebase.messaging)
}

This works on iOS somehow, but not on Android. Instrumented tests complain about FirebaseApp not being initialized. And as far as I know, I can't get around it because I can't do following setup:

@BeforeTest
fun initializeFirebase() {
    val app = Firebase.apps(context).firstOrNull() ?: Firebase.initialize(
        context,
        FirebaseOptions(
            applicationId = "1:846484016111:ios:dd1f6688bad7af768c841a",
            apiKey = "AIzaSyCK87dcMFhzCz_kJVs2cT2AVlqOTLuyWV0",
            databaseUrl = "https://fir-kotlin-sdk.firebaseio.com",
            storageBucket = "fir-kotlin-sdk.appspot.com",
            projectId = "fir-kotlin-sdk",
            gcmSenderId = "846484016111"
        )
    )

    // This does not exist
    messaging = Firebase.messaging(app)
}