test.dart

testWidgets('BackButtonListener takes priority over root back dispatcher', (WidgetTester tester) async {
    final SimpleRouteInformationProvider provider = SimpleRouteInformationProvider();
    provider.value = const RouteInformation(
      location: 'initial',
    );
    final BackButtonDispatcher outerDispatcher = RootBackButtonDispatcher();
    await tester.pumpWidget(buildBoilerPlate(
      Router<RouteInformation>(
        backButtonDispatcher: outerDispatcher,
        routeInformationProvider: provider,
        routeInformationParser: SimpleRouteInformationParser(),
        routerDelegate: SimpleRouterDelegate(
          builder: (BuildContext context, RouteInformation? information) {
            // Creates the sub-router.
            return Column(
              children: <Widget>[
                Text(information!.location!),
                BackButtonListener(
                  child: Container(),
                  onBackPressed: () {
                      provider.value = const RouteInformation(
                        location: 'popped inner1',
                      );
                      return SynchronousFuture<bool>(true);
                    },
                ),
              ],
            );
          },
          onPopRoute: () {
            provider.value = const RouteInformation(
              location: 'popped outter',
            );
            return SynchronousFuture<bool>(true);
          }
        ),
      )
    ));
   
    await tester.pumpWidget(buildBoilerPlate(
      Router<RouteInformation>(
        backButtonDispatcher: outerDispatcher,
        routeInformationProvider: provider,
        routeInformationParser: SimpleRouteInformationParser(),
        routerDelegate: SimpleRouterDelegate(
          builder: (BuildContext context, RouteInformation? information) {
            // Creates the sub-router.
            return Column(
              children: <Widget>[
                Text(information!.location!),
                BackButtonListener(
                  child: Container(),
                  onBackPressed: () {
                      provider.value = const RouteInformation(
                        location: 'a different call back',
                      );
                      return SynchronousFuture<bool>(true);
                    },
                ),
              ],
            );
          },
          onPopRoute: () {
            provider.value = const RouteInformation(
              location: 'popped outter',
            );
            return SynchronousFuture<bool>(true);
          }
        ),
      )
    ));
    // This should trigger didUpdateWidget
    await tester.pump();
  
    await tester.pumpWidget(buildBoilerPlate(
      Router<RouteInformation>(
        backButtonDispatcher: outerDispatcher,
        routeInformationProvider: provider,
        routeInformationParser: SimpleRouteInformationParser(),
        routerDelegate: SimpleRouterDelegate(
          builder: (BuildContext context, RouteInformation? information) {
            // Creates the sub-router.
            return Column(
              children: <Widget>[
                Text(information!.location!),
                Text('a different widget'),
              ],
            );
          },
          onPopRoute: () {
            provider.value = const RouteInformation(
              location: 'popped outter',
            );
            return SynchronousFuture<bool>(true);
          }
        ),
      )
    ));
    // This should trigger dispose
    await tester.pump();
  });