Migrate yet even more widget framework tests to null safety. (#67941)

Migrate yet even more widget framework tests to null safety.

packages/flutter/test/widgets/hit_testing_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/widgets.dart';

packages/flutter/test/widgets/html_element_view_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @TestOn('chrome')
 
 import 'dart:async';

packages/flutter/test/widgets/hyperlink_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/widgets.dart';

packages/flutter/test/widgets/icon_data_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
@@ -12,11 +10,11 @@ import 'package:flutter_test/flutter_test.dart';
 void main() {
   test('IconDataDiagnosticsProperty includes valueProperties in JSON', () {
     IconDataProperty property = IconDataProperty('foo', const IconData(101010));
-    final Map<String, Object> valueProperties = property.toJsonMap(const DiagnosticsSerializationDelegate())['valueProperties'] as Map<String, Object>;
+    final Map<String, Object> valueProperties = property.toJsonMap(const DiagnosticsSerializationDelegate())['valueProperties']! as Map<String, Object>;
     expect(valueProperties['codePoint'], 101010);
 
     property = IconDataProperty('foo', null);
-    final Map<String, Object> json = property.toJsonMap(const DiagnosticsSerializationDelegate());
+    final Map<String, Object?> json = property.toJsonMap(const DiagnosticsSerializationDelegate());
     expect(json.containsKey('valueProperties'), isFalse);
   });
 }

packages/flutter/test/widgets/icon_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
@@ -25,7 +23,7 @@ void main() {
       ),
     );
     final RichText text = tester.widget(find.byType(RichText));
-    expect(text.text.style.color, const Color(0xFF666666).withOpacity(0.5));
+    expect(text.text.style!.color, const Color(0xFF666666).withOpacity(0.5));
   });
 
   testWidgets('Icon sizing - no theme, default size', (WidgetTester tester) async {
@@ -125,7 +123,7 @@ void main() {
     );
 
     final RichText richText = tester.firstWidget(find.byType(RichText));
-    expect(richText.text.style.fontFamily, equals('Roboto'));
+    expect(richText.text.style!.fontFamily, equals('Roboto'));
   });
 
   testWidgets('Icon with semantic label', (WidgetTester tester) async {

packages/flutter/test/widgets/icon_theme_data_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 

packages/flutter/test/widgets/image_filter_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:typed_data';
 import 'dart:ui';
 
@@ -78,8 +76,7 @@ void main() {
 
     await pumpWithSigma(5.0);
     final RenderObject renderObject = tester.firstRenderObject(find.byType(ImageFiltered));
-    final ImageFilterLayer originalLayer = renderObject.debugLayer as ImageFilterLayer;
-    expect(originalLayer, isNotNull);
+    final ImageFilterLayer originalLayer = renderObject.debugLayer! as ImageFilterLayer;
 
     // Change blur sigma to force a repaint.
     await pumpWithSigma(10.0);

packages/flutter/test/widgets/image_headers_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:io';
 
@@ -25,7 +23,7 @@ void main() {
 
       expect(MockHttpHeaders.headers['flutter'], <String>['flutter']);
 
-    }, createHttpClient: (SecurityContext _) {
+    }, createHttpClient: (SecurityContext? _) {
       return client;
     });
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/57187
@@ -62,7 +60,7 @@ class MockHttpClientResponse extends Fake implements HttpClientResponse {
   HttpClientResponseCompressionState get compressionState => HttpClientResponseCompressionState.decompressed;
 
   @override
-  StreamSubscription<List<int>> listen(void Function(List<int> event) onData, {Function onError, void Function() onDone, bool cancelOnError}) {
+  StreamSubscription<List<int>> listen(void Function(List<int> event)? onData, {Function? onError, void Function()? onDone, bool? cancelOnError}) {
     return Stream<List<int>>.fromIterable(<List<int>>[kTransparentImage]).listen(
       onData,
       onDone: onDone,
@@ -78,6 +76,6 @@ class MockHttpHeaders extends Fake implements HttpHeaders {
   @override
   void add(String key, Object value, { bool preserveHeaderCase = false }) {
     headers[key] ??= <String>[];
-    headers[key].add(value.toString());
+    headers[key]!.add(value.toString());
   }
 }

packages/flutter/test/widgets/image_icon_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -12,7 +10,7 @@ import '../painting/mocks_for_image_cache.dart';
 
 
 void main() {
-  ImageProvider _image;
+  late ImageProvider _image;
 
   setUpAll(() async {
     _image = TestImageProvider(
@@ -45,8 +43,7 @@ void main() {
     );
 
     final Image image = tester.widget(find.byType(Image));
-    expect(image, isNotNull);
-    expect(image.color.alpha, equals(128));
+    expect(image.color!.alpha, equals(128));
   });
 
   testWidgets('ImageIcon sizing - no theme, explicit size', (WidgetTester tester) async {

packages/flutter/test/widgets/image_package_asset_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 

packages/flutter/test/widgets/image_resolution_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @TestOn('!chrome') // asset bundle behaves differently.
 import 'dart:typed_data';
 import 'dart:ui' as ui show Image;
@@ -43,7 +41,7 @@ class TestAssetBundle extends CachingAssetBundle {
 
   @override
   Future<ByteData> load(String key) {
-    ByteData data;
+    late ByteData data;
     switch (key) {
       case 'assets/image.png':
         data = TestByteData(1.0);
@@ -71,7 +69,7 @@ class TestAssetBundle extends CachingAssetBundle {
   Future<String> loadString(String key, { bool cache = true }) {
     if (key == 'AssetManifest.json')
       return SynchronousFuture<String>(manifest);
-    return SynchronousFuture<String>(null);
+    return SynchronousFuture<String>('');
   }
 
   @override
@@ -91,21 +89,20 @@ class TestAssetImage extends AssetImage {
 
   @override
   ImageStreamCompleter load(AssetBundleImageKey key, DecoderCallback decode) {
-    ImageInfo imageInfo;
+    late ImageInfo imageInfo;
     key.bundle.load(key.name).then<void>((ByteData data) {
       final TestByteData testData = data as TestByteData;
-      final ui.Image image = images[testData.scale];
+      final ui.Image image = images[testData.scale]!;
       assert(image != null, 'Expected ${testData.scale} to have a key in $images');
       imageInfo = ImageInfo(image: image, scale: key.scale);
     });
-    assert(imageInfo != null);
     return FakeImageStreamCompleter(
       SynchronousFuture<ImageInfo>(imageInfo)
     );
   }
 }
 
-Widget buildImageAtRatio(String imageName, Key key, double ratio, bool inferSize, Map<double, ui.Image> images, [ AssetBundle bundle ]) {
+Widget buildImageAtRatio(String imageName, Key key, double ratio, bool inferSize, Map<double, ui.Image> images, [ AssetBundle? bundle ]) {
   const double windowSize = 500.0; // 500 logical pixels
   const double imageSize = 200.0; // 200 logical pixels
 
@@ -313,12 +310,12 @@ void main() {
     await pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false, images, bundle));
     expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
     // Verify we got the 10x scaled image, since the TestByteData said it should be 10x.
-    expect(getRenderImage(tester, key).image.height, 480);
+    expect(getRenderImage(tester, key).image!.height, 480);
     key = GlobalKey();
     await pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true, images, bundle));
     expect(getRenderImage(tester, key).size, const Size(480.0, 480.0));
     // Verify we got the 10x scaled image, since the TestByteData said it should be 10x.
-    expect(getRenderImage(tester, key).image.height, 480);
+    expect(getRenderImage(tester, key).image!.height, 480);
   });
 
   testWidgets('Image cache resize upscale display 5', (WidgetTester tester) async {

packages/flutter/test/widgets/image_rtl_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:ui' as ui show Image;
 
 import 'package:flutter/foundation.dart';
@@ -31,7 +29,7 @@ class TestImageProvider extends ImageProvider<TestImageProvider> {
 }
 
 void main() {
-  ui.Image testImage;
+  late ui.Image testImage;
   setUpAll(() async {
     testImage = await createTestImage(width: 16, height: 9);
   });

packages/flutter/test/widgets/implicit_animations_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
@@ -20,7 +18,7 @@ const Duration animationDuration = Duration(milliseconds:1000);
 const Duration additionalDelay = Duration(milliseconds:1);
 
 void main() {
-  MockOnEndFunction mockOnEndFunction;
+  late MockOnEndFunction mockOnEndFunction;
   const Key switchKey = Key('switchKey');
 
   setUp(() {
@@ -355,7 +353,7 @@ void main() {
   });
 }
 
-Widget wrap({Widget child}) {
+Widget wrap({required Widget child}) {
   return Directionality(
     textDirection: TextDirection.ltr,
     child: Material(
@@ -366,16 +364,13 @@ Widget wrap({Widget child}) {
 
 class TestAnimatedWidget extends StatefulWidget {
   const TestAnimatedWidget({
-    Key key,
+    Key? key,
     this.callback,
-    this.switchKey,
-    this.state,
+    required this.switchKey,
+    required this.state,
   }) : super(key: key);
-  @required
-  final VoidCallback callback;
-  @required
+  final VoidCallback? callback;
   final Key switchKey;
-  @required
   final State<StatefulWidget> state;
 
   @override
@@ -408,7 +403,6 @@ abstract class _TestAnimatedWidgetState extends State<TestAnimatedWidget> {
   }
 }
 
-
 class _TestAnimatedContainerWidgetState extends _TestAnimatedWidgetState {
   @override
   Widget getAnimatedWidget() {
@@ -553,7 +547,7 @@ class _TestTweenAnimationBuilderWidgetState extends _TestAnimatedWidgetState {
       tween: Tween<double>(begin: 1, end: 2),
       duration: duration,
       onEnd: widget.callback,
-      builder: (BuildContext context, double size, Widget child) {
+      builder: (BuildContext context, double? size, Widget? child) {
         return Container(
           child: child,
           width: size,

packages/flutter/test/widgets/implicit_semantics_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter/rendering.dart';

packages/flutter/test/widgets/independent_widget_layout_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -13,7 +11,7 @@ const Size _kTestViewSize = Size(800.0, 600.0);
 class OffscreenRenderView extends RenderView {
   OffscreenRenderView() : super(
     configuration: const ViewConfiguration(size: _kTestViewSize),
-    window: WidgetsBinding.instance.window,
+    window: WidgetsBinding.instance!.window,
   );
 
   @override
@@ -32,7 +30,7 @@ class OffscreenWidgetTree {
   final RenderView renderView = OffscreenRenderView();
   final BuildOwner buildOwner = BuildOwner();
   final PipelineOwner pipelineOwner = PipelineOwner();
-  RenderObjectToWidgetElement<RenderBox> root;
+  RenderObjectToWidgetElement<RenderBox>? root;
 
   void pumpWidget(Widget app) {
     root = RenderObjectToWidgetAdapter<RenderBox>(
@@ -44,7 +42,7 @@ class OffscreenWidgetTree {
   }
 
   void pumpFrame() {
-    buildOwner.buildScope(root);
+    buildOwner.buildScope(root!);
     pipelineOwner.flushLayout();
     pipelineOwner.flushCompositingBits();
     pipelineOwner.flushPaint();
@@ -60,18 +58,18 @@ class Counter {
 }
 
 class Trigger {
-  VoidCallback callback;
+  VoidCallback? callback;
   void fire() {
     if (callback != null)
-      callback();
+      callback!();
   }
 }
 
 class TriggerableWidget extends StatefulWidget {
   const TriggerableWidget({
-    Key key,
-    this.trigger,
-    this.counter,
+    Key? key,
+    required this.trigger,
+    required this.counter,
   }) : super(key: key);
 
   final Trigger trigger;
@@ -110,8 +108,8 @@ class TriggerableState extends State<TriggerableWidget> {
 
 class TestFocusable extends StatefulWidget {
   const TestFocusable({
-    Key key,
-    this.focusNode,
+    Key? key,
+    required this.focusNode,
     this.autofocus = true,
   }) : super(key: key);
 

packages/flutter/test/widgets/inherited_dependencies_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/src/widgets/basic.dart';
 import 'package:flutter/src/widgets/framework.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -19,7 +17,7 @@ void main() {
         return const SizedBox();
       }),
     ));
-    final InheritedElement element = key.currentContext as InheritedElement;
+    final InheritedElement element = key.currentContext! as InheritedElement;
     expect(
       element.toStringDeep(minLevel: DiagnosticLevel.info),
       equalsIgnoringHashCodes(

packages/flutter/test/widgets/inherited_model_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 
 import 'package:flutter/foundation.dart';
@@ -13,28 +11,28 @@ import 'package:flutter/material.dart';
 // valued fields: a, b, c.
 class ABCModel extends InheritedModel<String> {
   const ABCModel({
-    Key key,
+    Key? key,
     this.a,
     this.b,
     this.c,
     this.aspects,
-    Widget child,
+    required Widget child,
   }) : super(key: key, child: child);
 
-  final int a;
-  final int b;
-  final int c;
+  final int? a;
+  final int? b;
+  final int? c;
 
   // The aspects (fields) of this model that widgets can depend on with
   // inheritFrom.
   //
   // This property is null by default, which means that the model supports
   // all 3 fields.
-  final Set<String> aspects;
+  final Set<String>? aspects;
 
   @override
   bool isSupportedAspect(Object aspect) {
-    return aspect == null || aspects == null || aspects.contains(aspect);
+    return aspect == null || aspects == null || aspects!.contains(aspect);
   }
 
   @override
@@ -50,13 +48,13 @@ class ABCModel extends InheritedModel<String> {
         || (c != old.c && dependencies.contains('c'));
   }
 
-  static ABCModel of(BuildContext context, { String fieldName }) {
+  static ABCModel? of(BuildContext context, { String? fieldName }) {
     return InheritedModel.inheritFrom<ABCModel>(context, aspect: fieldName);
   }
 }
 
 class ShowABCField extends StatefulWidget {
-  const ShowABCField({ Key key, this.fieldName }) : super(key: key);
+  const ShowABCField({ Key? key, required this.fieldName }) : super(key: key);
 
   final String fieldName;
 
@@ -69,8 +67,8 @@ class _ShowABCFieldState extends State<ShowABCField> {
 
   @override
   Widget build(BuildContext context) {
-    final ABCModel abc = ABCModel.of(context, fieldName: widget.fieldName);
-    final int value = widget.fieldName == 'a' ? abc.a : (widget.fieldName == 'b' ? abc.b : abc.c);
+    final ABCModel abc = ABCModel.of(context, fieldName: widget.fieldName)!;
+    final int? value = widget.fieldName == 'a' ? abc.a : (widget.fieldName == 'b' ? abc.b : abc.c);
     return Text('${widget.fieldName}: $value [${_buildCount++}]');
   }
 }
@@ -91,7 +89,7 @@ void main() {
         // aspect of the model changes.
         final Widget showABC = Builder(
           builder: (BuildContext context) {
-            final ABCModel abc = ABCModel.of(context);
+            final ABCModel abc = ABCModel.of(context)!;
             return Text('a: ${abc.a} b: ${abc.b} c: ${abc.c}');
           }
         );
@@ -193,7 +191,7 @@ void main() {
   });
 
   testWidgets('Looking up an non existent InheritedModel ancestor returns null', (WidgetTester tester) async {
-    ABCModel inheritedModel;
+    ABCModel? inheritedModel;
 
     await tester.pumpWidget(
       Builder(
@@ -228,8 +226,8 @@ void main() {
         // Which is the inner model, for which b,c are null.
         final Widget showABC = Builder(
           builder: (BuildContext context) {
-            final ABCModel abc = ABCModel.of(context);
-            return Text('a: ${abc.a} b: ${abc.b} c: ${abc.c}', style: Theme.of(context).textTheme.headline6);
+            final ABCModel abc = ABCModel.of(context)!;
+            return Text('a: ${abc.a} b: ${abc.b} c: ${abc.c}', style: Theme.of(context)!.textTheme.headline6);
           }
         );
 
@@ -330,7 +328,7 @@ void main() {
     int _a = 0;
     int _b = 1;
     int _c = 2;
-    Set<String> _innerModelAspects = <String>{'a'};
+    Set<String>? _innerModelAspects = <String>{'a'};
 
     // Same as in abcPage in the "Inner InheritedModel shadows the outer one"
     // test except: the "Add b aspect" changes adds 'b' to the set of
@@ -345,8 +343,8 @@ void main() {
         // Which is the inner model, for which b,c are null.
         final Widget showABC = Builder(
           builder: (BuildContext context) {
-            final ABCModel abc = ABCModel.of(context);
-            return Text('a: ${abc.a} b: ${abc.b} c: ${abc.c}', style: Theme.of(context).textTheme.headline6);
+            final ABCModel abc = ABCModel.of(context)!;
+            return Text('a: ${abc.a} b: ${abc.b} c: ${abc.c}', style: Theme.of(context)!.textTheme.headline6);
           }
         );
 

packages/flutter/test/widgets/inherited_test.dart

@@ -2,15 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 
 import 'test_widgets.dart';
 
 class TestInherited extends InheritedWidget {
-  const TestInherited({ Key key, Widget child, this.shouldNotify = true })
+  const TestInherited({ Key? key, required Widget child, this.shouldNotify = true })
     : super(key: key, child: child);
 
   final bool shouldNotify;
@@ -22,7 +20,7 @@ class TestInherited extends InheritedWidget {
 }
 
 class ValueInherited extends InheritedWidget {
-  const ValueInherited({ Key key, Widget child, this.value })
+  const ValueInherited({ Key? key, required Widget child, required this.value })
     : super(key: key, child: child);
 
   final int value;
@@ -32,7 +30,7 @@ class ValueInherited extends InheritedWidget {
 }
 
 class ExpectFail extends StatefulWidget {
-  const ExpectFail(this.onError, { Key key }) : super(key: key);
+  const ExpectFail(this.onError, { Key? key }) : super(key: key);
   final VoidCallback onError;
 
   @override
@@ -55,7 +53,7 @@ class ExpectFailState extends State<ExpectFail> {
 }
 
 class ChangeNotifierInherited extends InheritedNotifier<ChangeNotifier> {
-  const ChangeNotifierInherited({ Key key, Widget child, ChangeNotifier notifier })
+  const ChangeNotifierInherited({ Key? key, required Widget child, ChangeNotifier? notifier })
     : super(key: key, child: child, notifier: notifier);
 }
 
@@ -65,7 +63,7 @@ void main() {
 
     final Builder builder = Builder(
       builder: (BuildContext context) {
-        log.add(context.dependOnInheritedWidgetOfExactType<TestInherited>());
+        log.add(context.dependOnInheritedWidgetOfExactType<TestInherited>()!);
         return Container();
       }
     );
@@ -97,7 +95,7 @@ void main() {
           key: globalKey,
           child: Builder(
             builder: (BuildContext context) {
-              log.add(context.dependOnInheritedWidgetOfExactType<TestInherited>());
+              log.add(context.dependOnInheritedWidgetOfExactType<TestInherited>()!);
               return Container();
             }
           ),
@@ -134,7 +132,7 @@ void main() {
                       child: Container(
                         child: Builder(
                           builder: (BuildContext context) {
-                            final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
+                            final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>()!;
                             log.add('a: ${v.value}');
                             return const Text('', textDirection: TextDirection.ltr);
                           }
@@ -151,7 +149,7 @@ void main() {
                     child: Container(
                       child: Builder(
                         builder: (BuildContext context) {
-                          final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
+                          final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>()!;
                           log.add('b: ${v.value}');
                           return const Text('', textDirection: TextDirection.ltr);
                         }
@@ -209,7 +207,7 @@ void main() {
                         key: key,
                         child: Builder(
                           builder: (BuildContext context) {
-                            final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
+                            final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>()!;
                             log.add('a: ${v.value}');
                             return const Text('', textDirection: TextDirection.ltr);
                           }
@@ -227,7 +225,7 @@ void main() {
                       key: key,
                       child: Builder(
                         builder: (BuildContext context) {
-                          final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
+                          final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>()!;
                           log.add('b: ${v.value}');
                           return const Text('', textDirection: TextDirection.ltr);
                         }
@@ -270,7 +268,7 @@ void main() {
 
     final Widget child = Builder(
       builder: (BuildContext context) {
-        final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
+        final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>()!;
         log.add(v.value);
         return const Text('', textDirection: TextDirection.ltr);
       }
@@ -341,7 +339,7 @@ void main() {
     final Widget child = Builder(
       key: GlobalKey(),
       builder: (BuildContext context) {
-        final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
+        final ValueInherited v = context.dependOnInheritedWidgetOfExactType<ValueInherited>()!;
         log.add(v.value);
         return const Text('', textDirection: TextDirection.ltr);
       },
@@ -382,13 +380,13 @@ void main() {
   });
 
   testWidgets('Inherited widget notifies descendants when descendant previously failed to find a match', (WidgetTester tester) async {
-    int inheritedValue = -1;
+    int? inheritedValue = -1;
 
     final Widget inner = Container(
       key: GlobalKey(),
       child: Builder(
         builder: (BuildContext context) {
-          final ValueInherited widget = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
+          final ValueInherited? widget = context.dependOnInheritedWidgetOfExactType<ValueInherited>();
           inheritedValue = widget?.value;
           return Container();
         }

packages/flutter/test/widgets/inherited_theme_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -14,7 +12,7 @@ class TestRoute extends PageRouteBuilder<void> {
 }
 
 class IconTextBox extends StatelessWidget {
-  const IconTextBox(this.text, { Key key }) : super(key: key);
+  const IconTextBox(this.text, { Key? key }) : super(key: key);
   final String text;
   @override
   Widget build(BuildContext context) {
@@ -34,7 +32,7 @@ void main() {
     const Color textColor = Color(0xFF00FF00);
     const Color iconColor = Color(0xFF0000FF);
     bool useCaptureAll = false;
-    BuildContext navigatorContext;
+    late BuildContext navigatorContext;
 
     Widget buildFrame() {
       return WidgetsApp(
@@ -61,7 +59,7 @@ void main() {
                           behavior: HitTestBehavior.opaque,
                           onTap: () {
                             navigatorContext = context;
-                            Navigator.of(context).push(
+                            Navigator.of(context)!.push(
                               TestRoute(
                                 useCaptureAll
                                   ? InheritedTheme.captureAll(context, const IconTextBox('Hello'))
@@ -88,7 +86,7 @@ void main() {
           of: find.byType(Icon),
           matching: find.byType(RichText),
         ),
-      ).text.style;
+      ).text.style!;
     }
 
     TextStyle getTextStyle(String text) {
@@ -97,7 +95,7 @@ void main() {
           of: find.text(text),
           matching: find.byType(RichText),
         ),
-      ).text.style;
+      ).text.style!;
     }
 
     useCaptureAll = false;
@@ -123,7 +121,7 @@ void main() {
 
     // Return to the home route
     useCaptureAll = true;
-    Navigator.of(navigatorContext).pop();
+    Navigator.of(navigatorContext)!.pop();
     await tester.pumpAndSettle(); // route transition
 
     // Verify that all is the same as it was when the test started
@@ -199,7 +197,7 @@ void main() {
           of: find.byKey(key),
           matching: find.byType(RichText),
         ),
-      ).text.style;
+      ).text.style!;
     }
 
     expect(getIconStyle(icon1).color, innerColor);
@@ -245,7 +243,7 @@ void main() {
           of: find.text(text),
           matching: find.byType(RichText),
         ),
-      ).text.style;
+      ).text.style!;
     }
 
     expect(getTextStyle('Hello').fontSize, null);

packages/flutter/test/widgets/init_state_test.dart

@@ -2,15 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 
 List<String> ancestors = <String>[];
 
 class TestWidget extends StatefulWidget {
-  const TestWidget({ Key key }) : super(key: key);
+  const TestWidget({ Key? key }) : super(key: key);
   @override
   TestWidgetState createState() => TestWidgetState();
 }

packages/flutter/test/widgets/interactive_viewer_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
@@ -625,11 +623,11 @@ void main() {
 
     testWidgets('Scale with mouse returns onInteraction properties', (WidgetTester tester) async{
       final TransformationController transformationController = TransformationController();
-      Offset focalPoint;
-      Offset localFocalPoint;
-      double scaleChange;
-      Velocity currentVelocity;
-      bool calledStart;
+      late Offset focalPoint;
+      late Offset localFocalPoint;
+      late double scaleChange;
+      late Velocity currentVelocity;
+      late bool calledStart;
       await tester.pumpWidget(
         MaterialApp(
           home: Scaffold(
@@ -677,11 +675,11 @@ void main() {
 
     testWidgets('onInteraction can be used to get scene point', (WidgetTester tester) async{
       final TransformationController transformationController = TransformationController();
-      Offset focalPoint;
-      Offset localFocalPoint;
-      double scaleChange;
-      Velocity currentVelocity;
-      bool calledStart;
+      late Offset focalPoint;
+      late Offset localFocalPoint;
+      late double scaleChange;
+      late Velocity currentVelocity;
+      late bool calledStart;
       await tester.pumpWidget(
         MaterialApp(
           home: Scaffold(