anchor.diff:            );
     }
   }
  +
  +class DummyStatefulWidget extends StatefulWidget {
  +  const DummyStatefulWidget({Key? key}) : super(key: key);
  +
  +  @override
  +  State<StatefulWidget> createState() => DummyState();
  +}
  +
  +class DummyState extends State<DummyStatefulWidget> {
  +  @override
  +  Widget build(BuildContext context) => const SizedBox.expand();
  +}
  
positive.code:         child: OpenContainer(
            closedBuilder: (BuildContext context, VoidCallback action) {
              open = action;
              return Switch(
                value: true,
                onChanged: (bool v) {},
              );
            },
            openBuilder: (BuildContext context, VoidCallback action) {
              return const Text('Open');
  
negative.code:     navigator.pop();
      await tester.pump(const Duration(milliseconds: 200));
      expect(find.text('Closed'), findsOneWidget);
      final State stateClosing = tester.state(find.byType(DummyStatefulWidget));
      expect(stateClosing, isNotNull);
      expect(stateClosing, same(stateOpen));
    });
  