Flutter：如何模拟 Bloc

Question

I would like to mock my Bloc in order to test my view.

For example, this is my Bloc:

class SearchBloc extends Bloc<SearchEvent, SearchState> {
  @override
  // TODO: implement initialState
  SearchState get initialState => SearchStateUninitialized();

  @override
  Stream<SearchState> mapEventToState(SearchState currentState, SearchEvent event) async* {
    if (event is UserWrites) {
      yield (SearchStateInitialized.success(objects);
    }
  }
}

And this is the view:

class _SearchViewState extends State<SearchView> {
  final TextEditingController _filterController = new TextEditingController();

  @override
  void initState() {
    _filterController.addListener(() {
    widget._searchBloc.dispatch(FetchByName(_filterController.text));
     }
  }


 TextField buildAppBarTitle(BuildContext context) {
    return new TextField(
      key: Key("AppBarTextField"),
        controller: _filterController,
    );
  }

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: buildAppBarTitle(context),),
      body: buildBlocBuilder(),
    );
  }

BlocBuilder<SearchEvent, SearchState> buildBlocBuilder() {
    return BlocBuilder(
        bloc: widget._searchBloc,
        builder: (context, state) {
          if (state is SearchStateUninitialized) {
            return Container(
              key: Key("EmptyContainer"),
            );
          } 
            return buildInitializedView(state, context);
          }
        });

buildInitializedView(SearchStateInitialized state, BuildContext context) {
    if (state.objects.isEmpty) {
      return Center(child: Text("Nothing found"),);
    } else {
      return buildListOfCards();
    }
  }
    }

Now, this is my test:

testWidgets('Should find a card when the user searches for something', (WidgetTester tester) async {

  _searchView = new SearchView(_searchBloc);

    when(mockService.find( name: "a")).thenAnswer((_) =>
    [objects]);

    await tester.pumpWidget(generateApp(_searchView));
    await tester.enterText(find.byKey(Key("searchBar")), "a");
    await tester.pump();

    expect(find.byType(Card), findsOneWidget);
  });
}

As you can see, I just want to test that, when the user writes something in the search, and the object he's looking for exists, a card should be shown.

Answer 1

If I understood correctly, you are mocking some service that is used by the searchBloc. I personally try to design the app in a way that the app only depends on a bloc and the bloc may depend on some other services. Then when I would like to make a widget test, I only need to mock the bloc. You can use bloc_test package for that.

There is this example on the bloc_test page for stubbing a counterBloc:

// Create a mock instance
final counterBloc = MockCounterBloc();

// Stub the bloc `Stream`
whenListen(counterBloc, Stream.fromIterable([0, 1, 2, 3]));

however, I often do not need to stub the bloc stream and it is enough to emit the state, like this

when(counterBloc.state).thenAnswer((_) => CounterState(456));

Hope this helps.

Answer 2

Have a look at a post from David Anaya which deal with Unit Testing with “Bloc” and mockito.

The last version of his example is here

Answer 3

Sometimes widgets require a little time to build. Try with:

await tester.pumpWidget(generateApp(_searchView));
await tester.enterText(find.byKey(Key("searchBar")), "a");
await tester.pump(Duration(seconds: 1));

expect(find.byType(Card), findsOneWidget);

Answer 4

To mock the bloc, you can use the bloc_test package

Also, you may watch this tutorial which covers bloc testing include mock bloc very nice.