How to test navigation via Navigator in Flutter

While what Danny said is correct and works, you can also create a mocked NavigatorObserver to avoid any extra boilerplate:

import 'package:mockito/mockito.dart';class MockNavigatorObserver extends Mock implements NavigatorObserver {}

That would translate to your test case as follows:

void main() {  testWidgets('Button is present and triggers navigation after tapped',      (WidgetTester tester) async {    final mockObserver = MockNavigatorObserver();    await tester.pumpWidget(      MaterialApp(        home: MyScreen(),        navigatorObservers: [mockObserver],      ),    );    expect(find.byType(RaisedButton), findsOneWidget);    await tester.tap(find.byType(RaisedButton));    await tester.pumpAndSettle();    /// Verify that a push event happened    verify(mockObserver.didPush(any, any));    /// You'd also want to be sure that your page is now    /// present in the screen.    expect(find.byType(DetailsPage), findsOneWidget);  });}

I wrote an in-depth article about this on my blog, which you can find here.

In the navigator tests in the flutter repo they use the NavigatorObserver class to observe navigations:

class TestObserver extends NavigatorObserver {  OnObservation onPushed;  OnObservation onPopped;  OnObservation onRemoved;  OnObservation onReplaced;  @override  void didPush(Route<dynamic> route, Route<dynamic> previousRoute) {    if (onPushed != null) {      onPushed(route, previousRoute);    }  }  @override  void didPop(Route<dynamic> route, Route<dynamic> previousRoute) {    if (onPopped != null) {      onPopped(route, previousRoute);    }  }  @override  void didRemove(Route<dynamic> route, Route<dynamic> previousRoute) {    if (onRemoved != null)      onRemoved(route, previousRoute);  }  @override  void didReplace({ Route<dynamic> oldRoute, Route<dynamic> newRoute }) {    if (onReplaced != null)      onReplaced(newRoute, oldRoute);  }}

This looks like it should do what you want, however it may only work form the top level (MaterialApp), I'm not sure if you can provide it to just a widget.

Following solution is, let's say, a general approach and it's not specific to Flutter.

Navigation could be abstracted away from a screen or a widget. Test can mock and inject this abstraction. This approach should be sufficient for testing such behavior.

There are several ways how to achieve that. I will show one of those, for purpose of this response. Perhaps it's possible to simplify it a bit or to make it more "Darty".

Abstraction for navigation

class AppNavigatorFactory {  AppNavigator get(BuildContext context) =>      AppNavigator._forNavigator(Navigator.of(context));}class TestAppNavigatorFactory extends AppNavigatorFactory {  final AppNavigator mockAppNavigator;  TestAppNavigatorFactory(this.mockAppNavigator);  @override  AppNavigator get(BuildContext context) => mockAppNavigator;}class AppNavigator {  NavigatorState _flutterNavigator;  AppNavigator._forNavigator(this._flutterNavigator);  void showNextscreen() {    _flutterNavigator.pushNamed('/nextscreen');  }}

Injection into a widget

class MyScreen extends StatefulWidget {  final _appNavigatorFactory;  MyScreen(this._appNavigatorFactory, {Key key}) : super(key: key);  @override  _MyScreenState createState() => _MyScreenState(_appNavigatorFactory);}class _MyScreenState extends State<MyScreen> {  final _appNavigatorFactory;  _MyScreenState(this._appNavigatorFactory);  @override  Widget build(BuildContext context) {    return Scaffold(        body: Center(            child: RaisedButton(                onPressed: () {                    _appNavigatorFactory.get(context).showNextscreen();                },                child: Text(Strings.traktTvUrl)            )        )    );  }}

Example of a test (Uses Mockito for Dart)

class MockAppNavigator extends Mock implements AppNavigator {}void main() {  final appNavigator = MockAppNavigator();  setUp(() {    reset(appNavigator);  });  testWidgets('Button is present and triggers navigation after tapped',      (WidgetTester tester) async {    await tester.pumpWidget(MaterialApp(home: MyScreen(TestAppNavigatorFactory())));    expect(find.byType(RaisedButton), findsOneWidget);    await tester.tap(find.byType(RaisedButton));    verify(appNavigator.showNextscreen());  });}