I am new in TDD. I am writing a test for bloc in flutter and getting an error in the when method.

我是TDD的新手。我正在写一个测试，在颤动中的块，并得到了一个错误，当他的方法。

import 'package:bloc_test/bloc_test.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mockito/mockito.dart';
import 'package:weather_clean_architecture_tdd/presentation/bloc/weather_bloc.dart';
import 'package:weather_clean_architecture_tdd/presentation/screens/weather_page.dart';

class MockWeatherBloc extends MockBloc<WeatherEvent, WeatherState>
    implements WeatherBloc {}

class FakeWeatherState extends Fake implements WeatherState {}

class FakeWeatherEvent extends Fake implements WeatherEvent {}

void main() {
  late MockWeatherBloc mockWeatherBloc;

  setUp(() => mockWeatherBloc = MockWeatherBloc());

  Widget makeTestableWidget(Widget body) {
    return BlocProvider(
      create: (context) => mockWeatherBloc,
      child: MaterialApp(home: body),
    );
  }

  testWidgets(
    'text field trigger state to change from empty to loading',
    (widgetTester) async {
      // Arrange
      when(() => mockWeatherBloc.state).thenReturn(() => WeatherEmpty());

      // Act
      await widgetTester.pumpWidget(makeTestableWidget(const WeatherPage()));
      var textField = find.byType(TextField);
      expect(textField, findsOneWidget);
      await widgetTester.enterText(textField, 'Karachi');
      await widgetTester.pump();
      expect(find.text('Karachi'), findsOneWidget);
    },
  );
}

This is the error message I am getting
Bad state: No method stub was called from within when(). Was a real method called, or perhaps an
extension method?

这是我得到错误状态的错误消息：没有从When()内部调用方法存根。真正的方法是调用的，还是可能是扩展的方法？

I tried importing when of mocktail but still same error is being thrown.
I am expecting the test case to pass.

我尝试导入When of moackail，但仍然抛出相同的错误。我期待着测试用例能通过。

You could try

你可以试一试

when(() => mockWeatherBloc.stream)
    .thenAnswer((_) => const Stream.empty());
when(() => mockWeatherBloc.state).thenAnswer((_) =>WeatherEmpty()));
when(() => mockWeatherBloc.close()).thenAnswer((_) async {});

instead of

而不是

when(() => mockWeatherBloc.state).thenReturn(() => WeatherEmpty());