add e2e testing (#167)

Reviewed-on: #167

integration_test/helpers/fakes.dart

@@ -0,0 +1,47 @@
+import "dart:async";
+
+import "package:app_links_platform_interface/app_links_platform_interface.dart";
+import "package:url_launcher_platform_interface/link.dart";
+import "package:url_launcher_platform_interface/url_launcher_platform_interface.dart";
+
+/// Delivers links to the app as if the OS had opened them.
+class FakeAppLinks extends AppLinksPlatform {
+  final _links = StreamController<Uri>.broadcast();
+
+  void open(Uri uri) => _links.add(uri);
+
+  @override
+  Future<Uri?> getInitialLink() async => null;
+
+  @override
+  Future<String?> getInitialLinkString() async => null;
+
+  @override
+  Future<Uri?> getLatestLink() async => null;
+
+  @override
+  Future<String?> getLatestLinkString() async => null;
+
+  @override
+  Stream<Uri> get uriLinkStream => _links.stream;
+
+  @override
+  Stream<String> get stringLinkStream =>
+      _links.stream.map((uri) => uri.toString());
+}
+
+/// Hands launched URLs to [onLaunch] instead of opening a browser.
+class FakeUrlLauncher(final void Function(Uri url) onLaunch)
+    extends UrlLauncherPlatform {
+  @override
+  LinkDelegate? get linkDelegate => null;
+
+  @override
+  Future<bool> canLaunch(String url) async => true;
+
+  @override
+  Future<bool> launchUrl(String url, LaunchOptions options) async {
+    onLaunch(.parse(url));
+    return true;
+  }
+}