Test failing on BlocListener in flutter when testing widget

Question

I have two tests that check if a snack bar is showing when a login state is streamed and processed using the BlocListener.

void main() async {
  AuthenticationRepositoryMock _authenticationRepositoryMock;
  LoginBlocMock _loginBloc;
  final fireBaseUserMock = FirebaseUserMock();
  final randomValidPassword = "password";
  final buttonFinder = find.byKey(Key('credentials_button'));
  final snackBarFailureFinder = find.byKey(Key("snack_bar_failure"));
  final snackBarLoadingFinder = find.byKey(Key("snack_bar_loading"));
  final emailFieldFinder = find.byKey(Key('email_field'));
  final passwordFieldFinder = find.byKey(Key('password_field'));

  Widget makeTestableWidget() {
    return BlocProvider<LoginBloc>(
      builder: (context) => _loginBloc,
      child: MaterialApp(
        home: Scaffold(
          body: LoginPage(),
        )
      ),
    );
  }

  setUp((){
    _authenticationRepositoryMock = AuthenticationRepositoryMock();
    _loginBloc = LoginBlocMock(authenticationRepository: _authenticationRepositoryMock);
  });

  testWidgets('Show snack bar when state is LoginFailure', (WidgetTester tester) async {

    //Arrange
    var expectedStates = [
      LoginInitial(), 
      LoginFailure(error: "Could not find user. Please try different credentials")
    ];

    whenListen(_loginBloc, Stream.fromIterable(expectedStates));

    //Act
    await tester.pumpWidget(makeTestableWidget());

    expect(snackBarFailureFinder, findsNothing);

    await tester.enterText(emailFieldFinder, fireBaseUserMock.email);
    await tester.pumpAndSettle();

    await tester.enterText(passwordFieldFinder, randomValidPassword);
    await tester.pumpAndSettle();

    await tester.tap(buttonFinder);
    await tester.pumpAndSettle();

    //Assert
    expect(snackBarFailureFinder, findsOneWidget);
  });

  //FAILING FOR NO REASON!
  testWidgets('Show snack bar when state is LoginLoading', (WidgetTester tester) async {

    //Arrange
    var expectedStates = [
      LoginInitial(), 
      LoginLoading()
    ];

    whenListen(_loginBloc, Stream.fromIterable(expectedStates));

    //Act
    await tester.pumpWidget(makeTestableWidget());

    expect(snackBarLoadingFinder, findsNothing);

    await tester.enterText(emailFieldFinder, fireBaseUserMock.email);
    await tester.pumpAndSettle();

    await tester.enterText(passwordFieldFinder, randomValidPassword);
    await tester.pumpAndSettle();

    await tester.tap(buttonFinder);
    await tester.pumpAndSettle();

    //Assert
    expect(snackBarLoadingFinder, findsOneWidget);
  });
}

And these two tests are testing the following widget on the page:

BlocListener<LoginBloc, LoginState>(
              listener: (context, state){
                if(state is LoginFailure){
                  Scaffold.of(context)
                    .showSnackBar(SnackBar(
                      key: Key("snack_bar_failure"),
                      content: Row(
                        mainAxisAlignment: MainAxisAlignment.spaceBetween,
                        children: [Text('Login Failure'), Icon(Icons.error)],
                      ),
                      backgroundColor: Colors.redAccent
                    ));
                }

                if (state is LoginLoading) {
                  Scaffold.of(context)
                    .showSnackBar(SnackBar(
                      key: Key("snack_bar_loading"),
                      content: Row(
                        mainAxisAlignment: MainAxisAlignment.spaceBetween,
                        children: [Text('Logging in...'), Spinner()],
                      ),
                      backgroundColor: Colors.blueAccent
                    ));
                }
              }

The first test that looks up for the the snack bar with the key 'snack_bar_failure' passes, but the second test does not. It's literally the same test, same setup, only the expected states are different and the key of the snack bar is different snack_bar_loading.

The second test fails with the following error message:

The following TestFailure object was thrown running a test:
  Expected: exactly one matching node in the widget tree
  Actual: ?:<zero widgets with key [<'snack_bar_loading'>] (ignoring offstage widgets)>    
   Which: means none were found but one was expected

Am I missing something?

Felix Angelov · Accepted Answer · 2019-11-05 20:02:26Z

3

The question is answered in the issue (https://github.com/felangel/bloc/issues/655). Hope that helps!

answered Nov 5, 2019 at 20:02

Felix Angelov

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2 Comments

Mihai Neagoe Over a year ago

The only difference that I see from what you posted and my initial test is you used tester.pump() instead of tester.pumpAndSettle(). What is the difference between these two?

Felix Angelov Over a year ago

tester.pumpAndSettle repeatedly calls pump until there are no more scheduled frames whereas tester.pump only triggers a single frame. The main difference between what I posted and the original test is you had multiple pumpAndSettles which were both unnecessary and resulted in the SnackBar being shown and dismissed before the expect was executed.

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