如何使用未解决的 Future 对 FutureBuilder 进行小部件测试

Question

I wonder how I can test the case when a future is not yet completed in flutter widget tests.

The widget should show a spinner as long as the future is unresolved.

I tride this test case:

testWidgets(
  'should show a spinner when loading',
  (WidgetTester tester) async {
    when(valueRepository.getValues())
        .thenAnswer((_) => Future.delayed(Duration(seconds: 30), () => []));
    await tester.pumpWidget(withApp(ValueListPage(
      valueRepository: valueRepository,
    )));

    await tester.pumpAndSettle(
        Duration(seconds: 10), EnginePhase.build, Duration(minutes: 1));

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

Result: The future is resolved and the expectation fails.

Note: withApp initializes an App with localization. Because of that I have to call tester.pumpAndSettle() to wait for l10n.

Answer 1

I found a working solution with fakeAsync:

testWidgets(
  'should show a spinner when loading',
  (WidgetTester tester) async {
      when(valueRepository.getValues()).thenAnswer(
          (_) => Future.delayed(Duration(seconds: 1), () => []));
      await tester.pumpWidget(withApp(ValueListPage(
        valueRepository: valueRepository,
      )));

      await tester.pump();

      expect(find.byType(CircularProgressIndicator), findsOneWidget);
      await tester.pumpAndSettle();
      expect(find.byType(CircularProgressIndicator), findsNothing);
  },
);

Answer 2

Try

testWidgets(
  'should show a spinner when loading',
  (WidgetTester tester) async {
    tester.runAsync(() async {
      when(valueRepository.getValues())
          .thenAnswer((_) => Future.delayed(Duration(seconds: 30), () => []));
      await tester.pumpWidget(withApp(ValueListPage(
        valueRepository: valueRepository,
      )));

      await tester.pumpAndSettle(
          Duration(seconds: 10), EnginePhase.build, Duration(minutes: 1));

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

Tests run with fakeAsync by default and some async code doesn't run properly with fakeAsync.

Answer 3

Try to use completer to stay the AsyncSnapshot on waiting. for example:

testWidgets('should show a spinner when loading',(WidgetTester tester) async {

    Completer completer = Completer();
    when(valueRepository.getValues())
       .thenAnswer((_) => completer.future);
    await tester.pumpWidget(withApp(ValueListPage(
    valueRepository: valueRepository,
    )));

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