How to mock url_launcher package for flutter test?

Question

I used url_launcher: ^6.1.0 in my flutter project. I start to write tests for my widgets, but the part of widgets that used the url_launcher method to launch an URL, not worked properly when running the test.

One of the methods that I used inside my Widget is like below method:

 Future<void> _onTapLink(String? href) async {
    if (href == null) return;

    // canLaunchUrl method never return anything when we are calling this function inside flutter test
    if (await canLaunchUrl(Uri.parse(href))) {
      await launchUrl(Uri.parse(href));
    } else {
      print('cannot launch url: $href');
    }
  }

canLaunchUrl method never returns anything when we are calling this function inside the flutter test.

I'm looking for a way to mock the url_launcher package for using inside flutter tests.

Answer 1

To mock url_launcher you may:

1. Add plugin_platform_interface and url_launcher_platform_interface packages to dev_dependencies section in the pubspec.yaml file.
2. Implement the mock class. For example, with mocktail the implementation would be:

import 'package:mocktail/mocktail.dart';
import 'package:plugin_platform_interface/plugin_platform_interface.dart';
import 'package:url_launcher_platform_interface/url_launcher_platform_interface.dart';

class MockUrlLauncher extends Mock
    with MockPlatformInterfaceMixin
    implements UrlLauncherPlatform {}

Notice that here MockPlatformInterfaceMixin mixin is used.

3. Configure the mock as usual. With mocktail that might be:

MockUrlLauncher setupMockUrlLauncher() {
  final mock = MockUrlLauncher();
  registerFallbackValue(const LaunchOptions());

  when(() => mock.launchUrl(any(), any())).thenAnswer((_) async => true);
  return mock;
}

4. Tell url_launcher to use mocked version by setting it in UrlLauncherPlatform.instance:

final mock = setupMockUrlLauncher();
UrlLauncherPlatform.instance = mock;

Answer 2

This is an article that explicitly explains how to mock or fake the launchUrl function. Here is an example of how to mock it with mocktail. It also uses the ioc_container package to handle substitution with dependency injection.

import 'package:fafsdfsdf/main.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mocktail/mocktail.dart';
import 'package:url_launcher/url_launcher.dart';
import 'package:flutter/material.dart';

class LaunchMock extends Mock {
  Future<bool> call(
    Uri url, {
    LaunchMode? mode,
    WebViewConfiguration? webViewConfiguration,
    String? webOnlyWindowName,
  });
}

void main() {
  testWidgets('Test Url Launch', (tester) async {
    //These allow default values
    registerFallbackValue(LaunchMode.platformDefault);
    registerFallbackValue(const WebViewConfiguration());

    //Create the mock
    final mock = LaunchMock();
    when(() => mock(
          flutterDevUri,
          mode: any(named: 'mode'),
          webViewConfiguration: any(named: 'webViewConfiguration'),
          webOnlyWindowName: any(named: 'webOnlyWindowName'),
        )).thenAnswer((_) async => true);

    final builder = compose()
      //Replace the launch function with a mock
      ..addSingletonService<LaunchUrl>(mock);

    await tester.pumpWidget(
      builder.toContainer()<MyApp>(),
    );

    //Tap the icon
    await tester.tap(
      find.byIcon(Icons.favorite),
    );

    await tester.pumpAndSettle();

    verify(() => mock(flutterDevUri)).called(1);
  });
}