Emulator Unit Test Fails Saying "Unable to establish connection on channel" - flutter

Question

I use get_it for simple dependency injection. I have a function that I made sure is called when the app initializes as below:
void initDI() {
// ... the other providers and repositories ...
//--------- //
// Firebase //
//--------- //
// i reference these instances everywhere when i wanna access them
// such as providers, repositories, etc.
GetIt.I.registerLazySingleton<FirebaseAuth>(() => FirebaseAuth.instance);
GetIt.I.registerLazySingleton<FirebaseFirestore>(
() => FirebaseFirestore.instance,
);
GetIt.I.registerLazySingleton<FirebaseFunctions>(
() => FirebaseFunctions.instance,
);
}
In my test directory, I have a file named initializers.dart, which has setup functions for tests for convenience. One that concerns us is as follows:
// test/initializers.dart
Future<void> initFirebaseEmulatorUse() async {
// ensure widget bindings get initialized because firebase requires this for some reason
WidgetsFlutterBinding.ensureInitialized();
// initialize firebase app
await Firebase.initializeApp();
// use functions emulator because there is no mock or fake package for functions, which is reasonable
FirebaseFunctions.instance.useFunctionsEmulator('localhost', 5001);
// unregister default references
GetIt.I.unregister<FirebaseAuth>();
GetIt.I.unregister<FirebaseFirestore>();
// register with mocks and fakes
GetIt.I.registerLazySingleton<FirebaseAuth>(() => MockFirebaseAuth());
GetIt.I.registerLazySingleton<FirebaseFirestore>(
() => FakeFirebaseFirestore(),
);
}
And, an example test is as follows:
// import initializers, we'll need them
import '../initializers.dart';
void main() {
// use in setUpAll, once and for all
late FirebaseFirestore firebaseFirestore;
setUpAll(() {
// returning future here because i've seen setUpAll must return
// an instance of Future when it has to do something in the future
// so, marking it as async is not enough it seems
return Future(() async {
WidgetsFlutterBinding.ensureInitialized(); // just to be double sure
initDI();
await initFirebaseEmulatorUse();
firebaseFirestore = GetIt.I.get(); // get an instance of firestore
});
});
tearDownAll(() {
return Future(() async {
// ... do something to clear all documents in firestore? ...
// ... so it won't affect other tests? ...
// i need to access `firebaseFirestore` instance here to do it
});
});
test('do tests', () async {
// ... test stuff ...
});
}
However, this fails saying:
PlatformException(channel-error, Unable to establish connection on channel., null, null)
FirebaseCoreHostApi.initializeCore
✖ (setUpAll)
LateInitializationError: Local 'firebaseFirestore' has not been initialized.
dart:_internal LateError._throwLocalNotInitialized
main.<fn>.<fn>
===== asynchronous gap ===========================
dart:async new Future
main.<fn>
✖ (tearDownAll)
Exited (1)
When I go to the line where it throws this error, it actually throws in the tearDownAll.
Troubleshooting for a while, I think we've got two problems:
firebaseFirestore is not initialized while in tearDownAll. While I have it initialized in setUpAll, that probably means the Future I return from setUpAll does not finish fast enough until I reach tearDownAll. That's my guess.
That "Unable to establish connection on channel" message is, I believe, because somehow the Firebase cannot connect to my local emulator.
I've been trying to solve these with different methods for hours but couldn't find a way to solve it. Any blog post about setting up Firebase Emulator + Unit Testing is also appreciated. The posts that I've found so far couldn't get me figure out how I can connect to my local Firebase emulator. Thanks in advance.
Environment
Firebase Tools 11.19.0
get_it: ^7.2.0
firebase_core: ^2.3.0
firebase_auth: ^4.1.3
cloud_firestore: ^4.1.0
firebase_crashlytics: ^3.0.6
cloud_functions: ^4.0.5
firebase_analytics: ^10.0.6
fake_cloud_firestore: ^2.1.0 as dev
firebase_auth_mocks: ^0.9.2 as dev
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