classUser {String name;}voidmain() {testWidgets('basic', (WidgetTester tester)async {// Build our app and trigger a frame.await tester.pumpWidget(MyApp());expect(find.byWidgetPredicate((widget) {return widgetisDropdownButton<User>&& widget.value.name=="foo";    }), findsNothing);  });}

$ flutter test                  00:10 +0: Counter increments smoke test                                                                                                                                                                                                      00:11 +1: All tests passed!$ flutter test --platform chrome        org-dartlang-app:///widget_test.dart:22:61: Error: Property 'name' cannot be accessed on 'User?' because it is potentially null. - 'User' is from 'org-dartlang-app:///widget_test.dart'.Try accessing using ?. instead.      return widget is DropdownButton<User> && widget.value.name == "foo";                                                            ^^^^org-dartlang-app:///widget_test.dart:13:10: Error: Field 'name' should be initialized because its type 'String' doesn't allow null.  String name;         ^^^^Failed to compile

flutter analyzeAnalyzing flutter_playground...                                         No issues found! (ran in 2.2s)

flutter doctor -v[✓] Flutter (Channel beta, 1.25.0-8.3.pre, on Linux, locale fr_FR.UTF-8)    • Flutter version 1.25.0-8.3.pre at /home/william/Documents/flutter    • Framework revision 5d36f2e7f5 (il y a 2 semaines), 2021-01-14 15:57:49 -0800    • Engine revision 7a8f8ca02c    • Dart version 2.12.0 (build 2.12.0-133.7.beta)[!] Android toolchain - develop for Android devices (Android SDK version 30.0.2)    • Android SDK at /home/william/Android/Sdk    • Platform android-30, build-tools 30.0.2    • Java binary at: /usr/bin/java    • Java version OpenJDK Runtime Environment 18.9 (build 11.0.9.1+11)    ✗ Android license status unknown.      Run `flutter doctor --android-licenses` to accept the SDK licenses.      See https://flutter.dev/docs/get-started/install/linux#android-setup for more details.[✓] Chrome - develop for the web    • Chrome at google-chrome[!] Android Studio (not installed)    • Android Studio not found; download from https://developer.android.com/studio/index.html      (or visit https://flutter.dev/docs/get-started/install/linux#android-setup for detailed instructions).[✓] VS Code (version 1.52.1)    • VS Code at /usr/share/code    • Flutter extension can be installed from:      🔨 https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter[✓] Connected device (1 available)    • Chrome (web) • chrome • web-javascript • Google Chrome 88.0.4324.96! Doctor found issues in 2 categories.