Dart/Flutter - Extensions to emit ChangeNotifier changes as a Stream, very useful for unit testing

provider_generic_extensions.dart

/// Function to get the changed value everytime
typedef GetChangeFunction<T> = T Function();

extension AsStream<T> on ChangeNotifier {
  Stream<T> statusAsStream(GetChangeFunction<T> getChange) {
    final controller = StreamController<T>();

    // Redirect status changes into the Stream
    final notify = () => controller.add(getChange());
    addListener(notify);
    controller.onCancel = () => removeListener(notify);

    // As this is intended for tests it should close if no emitions were done
    // in x period of time to avoid a never ending test
    Future.delayed(Duration(seconds: 5)).then((value) => controller.close());

    return controller.stream;
  }

  StreamController<T> statusAsStreamController(GetChangeFunction<T> getChange) {
    final controller = StreamController<T>();

    // Redirect status changes into the Stream
    final notify = () => controller.add(getChange());
    addListener(notify);
    controller.onCancel = () => removeListener(notify);

    return controller;
  }
}

provider_viewmodel_extensions.dart

// Your ViewModel abstraction
abstract class ViewModel<S> with ChangeNotifier {
  S _status;

  S get status => _status;

  set status(S value) {
    _status = value;
    notifyListeners();
  }
}

// Cleaner extensions
extension AsStream<T> on ViewModel<T> {
  Stream<T> statusStream() {
    final controller = StreamController<T>();

    // Redirect status changes into the Stream
    final notify = () => controller.add(status);
    addListener(notify);
    controller.onCancel = () => removeListener(notify);

    // Timeout to cancel the stream if no changes
    Future.delayed(Duration(seconds: 5)).then((value) => controller.close());

    return controller.stream;
  }

  StreamController<T> statusStreamController() {
    final controller = StreamController<T>();

    // Redirect status changes into the Stream
    final notify = () => controller.add(status);
    addListener(notify);
    controller.onCancel = () => removeListener(notify);

    return controller;
  }
}