A little question about unit test in flutter

Question

I'm following the https://codelabs.developers.google.com/codelabs/flutter-app-testing and was stuck on step 6.

In function in file test/favorites_test.dart , the test fails if I changed the i+=2 to i++ and I don't know why. If the total items is less than 6, it can pass too. Why the number is so important in test.

It is a simple app, when tap the close button, just delete from list

//test/favorites_test.dart

Widget createFavoritesScreen() => ChangeNotifierProvider<Favorites>(
      create: (context) {
        favoritesList = Favorites();
        return favoritesList;
      },
      child: const MaterialApp(
        home: FavoritesPage(),
      ),
    );

void addItems() {
  for (var i = 0; i < 10; i += 2) {
    favoritesList.add(i);
  }
}

void main() {
  group('Favorites Page Widget Tests', () {
    testWidgets('Test if ListView shows up', (tester) async {
      await tester.pumpWidget(createFavoritesScreen());
      addItems();
      await tester.pumpAndSettle();
      expect(find.byType(ListView), findsOneWidget);
    });

    testWidgets('Testing Remove Button', (tester) async {
      await tester.pumpWidget(createFavoritesScreen());
      addItems();
      await tester.pumpAndSettle();
      var totalItems = tester.widgetList(find.byIcon(Icons.close)).length;
      await tester.tap(find.byIcon(Icons.close).first);
      await tester.pumpAndSettle();
      expect(tester.widgetList(find.byIcon(Icons.close)).length,
          lessThan(totalItems));
      expect(find.text('Removed from favorites.'), findsOneWidget);
    });
  });
}

Answer 1

Finally, I found the solution.

In testWidgets, the test runs in size (2400,1800) according to tester.view.physicalSize. (I don't know why the test page is not shown fully)

After tester.view.physicalSize = Size(10000, 10000), the test passed.

Don't forget to call tester.view.resetPhysicalSize() or it will affect the following widget tests.