anchor.diff:  
       expect(find.text('Page 1'), findsNothing);
       expect(find.text('Page 2'), isOnstage);
  -    verifyNever(navigatorObserver.didPop(any, any));
  -    verify(navigatorObserver.didStopUserGesture()).called(1);
  +    expect(navigatorObserver.invocations.removeLast(), NavigatorInvocation.didStopUserGesture);
  +    expect(navigatorObserver.invocations.removeLast(), isNot(NavigatorInvocation.didPop));
       expect(
         tester.state<NavigatorState>(find.byType(Navigator)).userGestureInProgress,
         false,
  
positive.code:   });
  }
  
  class MockNavigatorObserver extends Mock implements NavigatorObserver {}
  
  class PopupObserver extends NavigatorObserver {
    int popupCount = 0;
  
negative.code:     final TestGesture gesture = await tester.startGesture(const Offset(5, 200));
      // The width of the page.
      await gesture.moveBy(const Offset(800, 0));
      expect(navigatorObserver.invocations.removeLast(), NavigatorInvocation.didStartUserGesture);
      await gesture.up();
      await tester.pump();
  
      expect(find.text('Page 1'), isOnstage);
      expect(find.text('Page 2'), findsNothing);
      expect(navigatorObserver.invocations.removeLast(), NavigatorInvocation.didStopUserGesture);
      expect(navigatorObserver.invocations.removeLast(), NavigatorInvocation.didPop);
    });
  
    testWidgets('test edge swipe then drop back at starting point works', (WidgetTester tester) async {
  