How to properly extend DatabaseReference in Firebase iOS SDK v4 - ios

Question

I have an app that was originally developed in Swift 2 / Xcode 7.3.1 using the Firebase iOS SDK v2.5.1 which is currently being updated to the latest versions of Swift/Xcode, which entails also updating the Firebase SDK.
We have hundreds of unit tests that were developed that, for the most part have been easy to update, but there are a few in particular that are tricky due to the way the old Firebase SDK was structured (and thus how it was used).
Originally, because nearly all Firebase database functionality was encompassed in one "Firebase" class, we created a custom class that inherited from the Firebase class that overrode several methods. In the latest SDK, functionality has been split further into different classes (namely the separate of Database and DatabaseReference), and most of the methods that were overridden are now a part of the DatabaseReference class in the FirebaseDatabase framework.
To make this a bit more tangible.
Old code:
class FirebaseTest: Firebase {
override func childByAutoId() {
//generate and save Auto ID internally to be used later for testing/validation
super.childByAutoID();
}
//many other overridden methods
}
//Unit tests
let fbref = FirebaseTest(url: "my-firebase.firebaseio.com/test");
// etc
The old Firebase SDK would return a Firebase reference to the base URL provided in the constructor, and because many of the properties we used were members of Firebase, all of our testing worked.
Following the SDK migration guide, I end up with the following code (simply replacing Firebase with DatabaseReference):
class FirebaseTest: DatabaseReference {
override func childByAutoId() {
//generate and save Auto ID internally to be used later for testing/validation
super.childByAutoID();
}
//many other overridden methods
}
//Unit tests
let fbref = FirebaseTest(fromUrl: "my-firebase.firebaseio.com/test")
// etc
Now, immediately, there is a problem with the above code that prevents it from compiling: the DatabaseReference constructor does not take any arguments. I can change it to the following
let fbref = FirebaseTest();
but now I know that, while it will compile, the tests will absolutely fail. The tricky part is that, in the latest SDK, database references are only supposed to be retrieved from a Database as follows:
//don't do this!
let fbref = DatabaseReference(); //will compile, but will break at runtime. Upon inspection in the debugger, there are several internal properties that should be set that are null. Those internal properties are likely all set correctly if the database reference is obtained correctly
//do it one of these ways
let fbref2 = Database.database().reference();
let fbref3 = Database.database().reference(fromUrl: "my-firebase.firebaseio.com/test") //also have access to this "reference(fromUrl: )" method from Database.database()
let fbref4 = Database.database().reference(withPath: "/test") //also have access to this "reference(withPath: )" method from Database.database()
So, hopefully my conundrum is becoming clear -- because I can only retrieve a correctly-initalized DatabaseReference from a Database, rather than my version of DatabaseReference that has overridden methods for testing, I'm fairly stuck.
Also, I have looked into creating an extension of Database itself as follows:
class FirebaseTest: DatabaseReference {
override func childByAutoId() {
//generate and save Auto ID internally to be used later for testing/validation
super.childByAutoID();
}
//many other overridden methods
}
class FirebaseDatabaseTest: Database {
override func reference(fromUrl: String) {
return FirebaseTest();
}
}
let fbref = FirebaseDatabaseTest().reference(fromUrl: "my-firebase.firebaseio.com/test")
But, even though I am intercepting the url in the overridden reference method, there's no clear way for me to "set up" the DatabaseReference the correct way using that URL.
Thoughts?