Question 221960 in Flutter Question posted in
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Flutter unit test question. How to test local variable is changed?

/// A flag that indicates whether the NotificationProvider is being processed.
  bool _isProcess = false;

  set isProcess(bool value) {
    _isProcess = value;
    notifyListeners();
  }

  bool get isProcess => _isProcess;

  NotificationProvider({required this.fetchNotificationUseCase});

  //TODO("Satoshi"): catch exception or error
  /// Fetch notification from api-server.
  Future<void> fetchNotification() async {
    try {
      isProcess = true;
      final res = await fetchNotificationUseCase.fetchNotification();

      notificationList.clear();
      notificationList.addAll(res);

      isProcess = false;
      notifyListeners();
    } catch (e) {
      isProcess = false;
      notifyListeners();
      debugPrint(e.toString());
    }
  }

I want to test isProcess property is changed to true and false. But the only I can test is just isProcess is false after fetchNotification method is completed.
How to test isProcess’s change ?

This is a test code what I wrote

  test('then isProcess is being false', () async {
    await notificationProvider.fetchNotification();

    expect(notificationProvider.isProcess, false);
  });
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2

Answers


  1. 0

    You can watch value changing using addListener method in ChangeNotifier.

    sample code

    test('isProcess changes true then false', () async {
  expect(notificationProvider.isProcess, false);
  int listenerCounts = 0;
  List<bool> matches = [true, false];
  final listener = () {
    expect(notificationProvider.isProcess, matches[listenerCounts]);
    listenerCounts++;
  }
  notificationProvider.addListener(listener);
  await notificationProvider.fetchNotification();
  notificationProvider.removeListener(listener);
});
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  2. 0

    fetchNotification synchronously sets isProcess = true before doing asynchronous work. You therefore can synchronously check that notificationProvider.isProcess transitions from false to true and then check that it returns to false after all asynchronous work completes:

      test('then isProcess is being false', () async {
    expect(notificationProvider.isProcess, false);
    var future = notificationProvider.fetchNotification();
    expect(notificationProvider.isProcess, true);
    await future;
    expect(notificationProvider.isProcess, false);
  });
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