带有 flutter_bloc 的 Flutter testWidgets - 测试仅在一起执行时失败

Question

我在 flutter 中对附加的小部件测试有问题。当我运行单独测试时，每个测试都成功；但是，当我运行整个 main() 方法时，前三个测试成功但后两个测试失败，但出现以下异常：

Expected: exactly one matching node in the widget tree
  Actual: ?:<zero widgets with type "SuccessDialog" (ignoring offstage widgets)>

我知道异常意味着我期待的小部件不存在 - 我不明白的是为什么测试在单独运行时成功但在运行之后失败其他测试。每次测试后有没有我需要 "resetting" 的情况？

我试过在每个测试开始时插入 "final SemanticsHandle handle = tester.ensureSemantics();" 并在每个测试结束时插入 "handle.dispose();" 但得到的结果相同。

编辑： 经过进一步调查，问题似乎出在我如何使用 flutter_bloc 包管理 bloc 实例。我已经改变了我的测试，为每个测试创建一个新的 testWidget 实例，但我仍然遇到同样的问题。是否有任何我可能遗漏的东西会导致 bloc 实例在 testWidget 对象中持续存在？

我的新测试代码如下所示：

main() {
  MvnoMockClient.init();

  testWidgets(
      'Voucher Redemption: Tapping redeem when no values were entered yields 2 field errors',
      (WidgetTester tester) async {
    Widget testWidget = MediaQuery(
      data: MediaQueryData(),
      child: MaterialApp(
        home: VoucherRedemptionPage(onSuccess: () {}, onFail: () {}),
      ),
    );
    await tester.pumpWidget(testWidget);

    await tester.tap(find.byType(PrimaryCardButton));
    await tester.pump();

    expect(find.text("Field is required"), findsNWidgets(2));
  });

  testWidgets(
      'Voucher Redemption: Tapping redeem when only voucher number was entered yields one field error',
      (WidgetTester tester) async {
    Widget testWidget = MediaQuery(
      data: MediaQueryData(),
      child: MaterialApp(
        home: VoucherRedemptionPage(onSuccess: () {}, onFail: () {}),
      ),
    );
    await tester.pumpWidget(testWidget);

    await tester.enterText(find.byType(PlainTextField), "0000000000");
    await tester.tap(find.byType(PrimaryCardButton));
    await tester.pump();

    expect(find.text("Field is required"), findsOneWidget);
  });

  testWidgets(
      'Voucher Redemption: Tapping redeem when only mobile number was entered yields one field error',
      (WidgetTester tester) async {
    Widget testWidget = MediaQuery(
      data: MediaQueryData(),
      child: MaterialApp(
        home: VoucherRedemptionPage(onSuccess: () {}, onFail: () {}),
      ),
    );
    await tester.pumpWidget(testWidget);

    await tester.enterText(find.byType(MsisdnField), "0815029249");
    await tester.tap(find.byType(PrimaryCardButton));
    await tester.pump();

    expect(find.text("Field is required"), findsOneWidget);
  });

  testWidgets(
      'Voucher Redemption: A successful server response yields a success dialog',
      (WidgetTester tester) async {
    Widget testWidget = MediaQuery(
      data: MediaQueryData(),
      child: MaterialApp(
        home: VoucherRedemptionPage(onSuccess: () {}, onFail: () {}),
      ),
    );
    await tester.pumpWidget(testWidget);

    await tester.enterText(find.byType(PlainTextField), "0000000000");
    await tester.enterText(find.byType(MsisdnField), "0815029249");
    await tester.tap(find.text("REDEEM"));
    await tester.pump();

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

  testWidgets(
      'Voucher Redemption: An unsuccessful server response yields an error dialog',
      (WidgetTester tester) async {
    Widget testWidget = MediaQuery(
      data: MediaQueryData(),
      child: MaterialApp(
        home: VoucherRedemptionPage(onSuccess: () {}, onFail: () {}),
      ),
    );
    await tester.pumpWidget(testWidget);

    gToken = "invalid";
    await tester.enterText(find.byType(PlainTextField), "0000000000");
    await tester.enterText(find.byType(MsisdnField), "0815029249");
    await tester.tap(find.byType(PrimaryCardButton));
    await tester.pump();
    gToken = "validToken";

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

作为额外参考，我还在下面包含了 VoucherRedemptionPage 和 VoucherRedemptionScreen 的代码：

class VoucherRedemptionPage extends StatelessWidget {
  final onSuccess;
  final onFail;

  const VoucherRedemptionPage({Key key, @required this.onSuccess, @required this.onFail})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    var _voucherRedemptionBloc = new VoucherRedemptionBloc();
    return Container(
      decoration: BoxDecoration(
        image: DecorationImage(
            image: AssetImage("assets/" + gFlavor + "/primary_background.png"),
            fit: BoxFit.cover),
      ),
      child: new Scaffold(
        backgroundColor: Colors.transparent,
        appBar: new AppBar(
          title: new Text(gDictionary.find("Redeem Voucher")),
        ),
        body: new VoucherRedemptionScreen(
          voucherRedemptionBloc: _voucherRedemptionBloc,
          onSuccess: this.onSuccess,
          onFail: this.onFail,
        ),
      ),
    );
  }
}


class VoucherRedemptionScreen extends StatefulWidget {
  const VoucherRedemptionScreen({
    Key key,
    @required VoucherRedemptionBloc voucherRedemptionBloc,
    @required this.onSuccess,
    @required this.onFail,
  })  : _voucherRedemptionBloc = voucherRedemptionBloc,
        super(key: key);

  final VoucherRedemptionBloc _voucherRedemptionBloc;
  final onSuccess;
  final onFail;

  @override
  VoucherRedemptionScreenState createState() {
    return new VoucherRedemptionScreenState(
        _voucherRedemptionBloc, onSuccess, onFail);
  }
}

class VoucherRedemptionScreenState extends State<VoucherRedemptionScreen> {
  final VoucherRedemptionBloc _voucherRedemptionBloc;
  final onSuccess;
  final onFail;
  TextEditingController _msisdnController = TextEditingController();
  TextEditingController _voucherPinController = TextEditingController();
  GlobalKey<FormState> _formKey = GlobalKey<FormState>();

  VoucherRedemptionScreenState(
      this._voucherRedemptionBloc, this.onSuccess, this.onFail);

  @override
  void initState() {
    super.initState();
  }

  @override
  void dispose() {
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return BlocBuilder<VoucherRedemptionEvent, VoucherRedemptionState>(
      bloc: _voucherRedemptionBloc,
      builder: (
        BuildContext context,
        VoucherRedemptionState currentState,
      ) {
        if (currentState is VoucherRedemptionInitial) {
          _voucherPinController.text = currentState.scannedNumber;
          return _buildFormCard();
        }

        if (currentState is VoucherRedemptionLoading) {
          return Center(
            child: CircularProgressIndicator(),
          );
        }

        if (currentState is VoucherRedemptionSuccess) {
          return SuccessDialog(
            title: gDictionary.find("Voucher Redeemed Successfully"),
            description: currentState.successMessage,
            closeText: gDictionary.find("OK"),
            closeAction: () {
              this.onSuccess();
              _voucherRedemptionBloc.dispatch(ResetVoucherRedemptionState());
            },
          );
        }

        if (currentState is VoucherRedemptionError) {
          return ErrorDialog(
            errorCode: currentState.errorCode,
            errorMessage: currentState.errorMessage,
            closeText: gDictionary.find("OK"),
            closeAction: () {
              this.onFail();
              _voucherRedemptionBloc.dispatch(ResetVoucherRedemptionState());
            },
          );
        }
      },
    );
  }

  Widget _buildFormCard() {
    return Container(
      decoration: BoxDecoration(
          color: Colors.white,
          borderRadius: BorderRadius.only(
              topLeft: Radius.circular(8), topRight: Radius.circular(8))),
      padding: EdgeInsets.fromLTRB(12, 12, 12, 0),
      width: double.infinity,
      height: double.infinity,
      child: _buildCardContent(),
    );
  }

  Widget _buildCardContent() {
    return SingleChildScrollView(
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          Text(
            gDictionary.find("Transaction Amount"),
            style: TextStyle(
                fontSize: 14,
                color: Theme.of(context).primaryColorDark,
                fontWeight: FontWeight.bold),
          ),
          Container(height: 16),
          Form(
            key: _formKey,
            child: _buildFormContent(),
          ),
        ],
      ),
    );
  }

  Column _buildFormContent() {
    return Column(
      children: <Widget>[
        PlainTextField(
          controller: _voucherPinController,
          label: gDictionary.find("Voucher Number"),
          required: true,
        ),
        Container(height: 16),
        MsisdnField(
          controller: _msisdnController,
          label: gDictionary.find("Mobile Number"),
          required: true,
        ),
        Divider(),
        Row(
          mainAxisAlignment: MainAxisAlignment.end,
          children: <Widget>[
            SecondaryCardButton(
              text: gDictionary.find("SCAN VOUCHER"),
              onPressed: () {
                _voucherRedemptionBloc.dispatch(
                  ScanBarcode(),
                );
              },
            ),
            Container(
              width: 8.0,
            ),
            PrimaryCardButton(
              text: gDictionary.find("REDEEM"),
              onPressed: () {
                if (_formKey.currentState.validate()) {
                  _voucherRedemptionBloc.dispatch(
                    RedeemVoucher(
                      _voucherPinController.text,
                      _msisdnController.text,
                    ),
                  );
                }
              },
            ),
          ],
        )
      ],
    );
  }
}

Answer 1

这可能是因为您的测试改变了一些全局变量但没有重置它们的值。

确保安全的一种方法是始终使用 setUp 和 tearDown 而不是直接在 main 范围内改变变量：

int global = 0;

void main() {
  final initialGlobalValue = global;
  setUp(() {
    global = 42;
  });
  tearDown(() {
    global = initialGlobalValue;
  });


  test('do something with "global"', () {
    expect(++global, 43);
  });

  test('do something with "global"', () {
    // would fail without setUp/tearDown
    expect(++global, 43);
  });
}

同样，如果测试需要修改变量，请使用 addTearDown 而不是稍后在测试中手动重置值。

不要:

int global = 0;
test("don't", () {
  global = 43;
  expect(global, 43);
  global = 0;
})

DO:

int global = 0;
test('do', () {
  global = 43;
  addTearDown(() => global = 0);

  expect(global, 43);     
});

这确保即使测试失败，该值也将始终被重置——以便其他测试正常运行。

Answer 2

找到问题了。我在创建 bloc 的实例时使用了单例模式——这导致状态在不同的小部件对象中持续存在。很少有人会遇到与我相同的问题，但下面是我为缓解问题而更改的代码

旧有问题的代码：

class VoucherRedemptionBloc
    extends Bloc<VoucherRedemptionEvent, VoucherRedemptionState> {
  static final VoucherRedemptionBloc _voucherRedemptionBlocSingleton =
      new VoucherRedemptionBloc._internal();
  factory VoucherRedemptionBloc() {
    return _voucherRedemptionBlocSingleton;
  }
  VoucherRedemptionBloc._internal();

  //...
}

更新的工作代码：

class VoucherRedemptionBloc
    extends Bloc<VoucherRedemptionEvent, VoucherRedemptionState> {
  VoucherRedemptionBloc();

  //...
}

Answer 3

在我的例子中，我没有设置 skipOffstage: false，做这样的事情对我有用：

expect(find.text('text', skipOffstage: false), findsNWidgets(2));

带有 flutter_bloc 的 Flutter testWidgets - 测试仅在一起执行时失败

Flutter testWidgets with flutter_bloc - tests fail only when executed together

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