Migrate some widget tests to NNBD (#68150)

packages/flutter/lib/src/widgets/sliver.dart

@@ -213,11 +213,13 @@ class _SaltedValueKey extends ValueKey<Key>{
   const _SaltedValueKey(Key key): assert(key != null), super(key);
 }
 
-/// Called to find the new index of a child based on its key in case of
+/// Called to find the new index of a child based on its `key` in case of
 /// reordering.
 ///
+/// If the child with the `key` is no longer present, null is returned.
+///
 /// Used by [SliverChildBuilderDelegate.findChildIndexCallback].
-typedef ChildIndexGetter = int Function(Key key);
+typedef ChildIndexGetter = int? Function(Key key);
 
 /// A delegate that supplies children for slivers using a builder callback.
 ///
@@ -424,8 +426,8 @@ class SliverChildBuilderDelegate extends SliverChildDelegate {
   /// when the order in which children are returned from [builder] changes.
   /// This may result in state-loss.
   ///
-  /// This callback should take an input [Key], and It should return the
-  /// index of the child element with associated key, null if not found.
+  /// This callback should take an input [Key], and it should return the
+  /// index of the child element with that associated key, or null if not found.
   final ChildIndexGetter? findChildIndexCallback;
 
   @override

packages/flutter/test/widgets/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 'dart:math';
 import 'dart:ui';
 
@@ -21,7 +19,7 @@ void main() {
   });
 
   testWidgets('Semantics shutdown and restart', (WidgetTester tester) async {
-    SemanticsTester semantics = SemanticsTester(tester);
+    SemanticsTester? semantics = SemanticsTester(tester);
 
     final TestSemantics expectedSemantics = TestSemantics.root(
       children: <TestSemantics>[
@@ -436,7 +434,7 @@ void main() {
     expect(semantics, hasSemantics(expectedSemantics));
 
     // Do the actions work?
-    final SemanticsOwner semanticsOwner = tester.binding.pipelineOwner.semanticsOwner;
+    final SemanticsOwner semanticsOwner = tester.binding.pipelineOwner.semanticsOwner!;
     int expectedLength = 1;
     for (final SemanticsAction action in allActions) {
       switch (action) {
@@ -574,7 +572,7 @@ void main() {
       ],
     );
 
-    final SemanticsOwner semanticsOwner = tester.binding.pipelineOwner.semanticsOwner;
+    final SemanticsOwner semanticsOwner = tester.binding.pipelineOwner.semanticsOwner!;
 
     expect(semantics, hasSemantics(expectedSemantics));
     semanticsOwner.performAction(expectedId, SemanticsAction.tap);
@@ -1101,5 +1099,5 @@ void main() {
 }
 
 class CustomSortKey extends OrdinalSortKey {
-  const CustomSortKey(double order, {String name}) : super(order, name: name);
+  const CustomSortKey(double order, {String? name}) : super(order, name: name);
 }

packages/flutter/test/widgets/semantics_tester_generateTestSemanticsExpressionForCurrentSemanticsTree_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:io';
 
@@ -62,10 +60,10 @@ void _tests() {
       .join('\n')
       .trim() + ',';
 
-    File findThisTestFile(Directory directory) {
+    File? findThisTestFile(Directory directory) {
       for (final FileSystemEntity entity in directory.listSync()) {
         if (entity is Directory) {
-          final File childSearch = findThisTestFile(entity);
+          final File? childSearch = findThisTestFile(entity);
           if (childSearch != null) {
             return childSearch;
           }
@@ -76,7 +74,7 @@ void _tests() {
       return null;
     }
 
-    final File thisTestFile = findThisTestFile(Directory.current);
+    final File thisTestFile = findThisTestFile(Directory.current)!;
     expect(thisTestFile, isNotNull);
     String expectedCode = thisTestFile.readAsStringSync();
     expectedCode = expectedCode.substring(

packages/flutter/test/widgets/semantics_tester_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/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/widgets/semantics_traversal_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:collection';
 import 'dart:math' as math;
 import 'dart:ui';
@@ -293,9 +291,9 @@ class TraversalTester {
   final SemanticsTester semantics;
 
   Future<void> test({
-    TextDirection textDirection,
-    Map<String, Rect> children,
-    String expectedTraversal,
+    required TextDirection textDirection,
+    required Map<String, Rect> children,
+    required String expectedTraversal,
   }) async {
     assert(children is LinkedHashMap);
     await tester.pumpWidget(
@@ -314,8 +312,8 @@ class TraversalTester {
                         explicitChildNodes: true,
                         label: label,
                         child: SizedBox(
-                          width: children[label].width,
-                          height: children[label].height,
+                          width: children[label]!.width,
+                          height: children[label]!.height,
                         ),
                       ),
                     );

packages/flutter/test/widgets/semantics_zero_surface_size_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/rendering.dart';
 import 'package:flutter/widgets.dart';

packages/flutter/test/widgets/set_state_1_test.dart

@@ -2,13 +2,11 @@
 // 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';
 
 class Inside extends StatefulWidget {
-  const Inside({ Key key }) : super(key: key);
+  const Inside({ Key? key }) : super(key: key);
   @override
   InsideState createState() => InsideState();
 }
@@ -29,11 +27,11 @@ class InsideState extends State<Inside> {
 
 class Middle extends StatefulWidget {
   const Middle({
-    Key key,
+    Key? key,
     this.child,
   }) : super(key: key);
 
-  final Inside child;
+  final Inside? child;
 
   @override
   MiddleState createState() => MiddleState();
@@ -54,7 +52,7 @@ class MiddleState extends State<Middle> {
 }
 
 class Outside extends StatefulWidget {
-  const Outside({ Key key }) : super(key: key);
+  const Outside({ Key? key }) : super(key: key);
   @override
   OutsideState createState() => OutsideState();
 }

packages/flutter/test/widgets/set_state_2_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/widgets.dart';
 

packages/flutter/test/widgets/set_state_3_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';
 
-ChangerState changer;
+late ChangerState changer;
 
 class Changer extends StatefulWidget {
-  const Changer(this.child, { Key key }) : super(key: key);
+  const Changer(this.child, { Key? key }) : super(key: key);
 
   final Widget child;
 
@@ -34,7 +32,7 @@ class ChangerState extends State<Changer> {
 }
 
 class Wrapper extends StatelessWidget {
-  const Wrapper(this.child, { Key key }) : super(key: key);
+  const Wrapper(this.child, { Key? key }) : super(key: key);
 
   final Widget child;
 
@@ -43,7 +41,7 @@ class Wrapper extends StatelessWidget {
 }
 
 class Leaf extends StatefulWidget {
-  const Leaf({ Key key }) : super(key: key);
+  const Leaf({ Key? key }) : super(key: key);
   @override
   LeafState createState() => LeafState();
 }

packages/flutter/test/widgets/set_state_4_test.dart

@@ -2,13 +2,11 @@
 // 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';
 
 class Changer extends StatefulWidget {
-  const Changer({ Key key }) : super(key: key);
+  const Changer({ Key? key }) : super(key: key);
   @override
   ChangerState createState() => ChangerState();
 }

packages/flutter/test/widgets/set_state_5_test.dart

@@ -2,13 +2,11 @@
 // 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';
 
 class BadWidget extends StatefulWidget {
-  const BadWidget({ Key key }) : super(key: key);
+  const BadWidget({ Key? key }) : super(key: key);
   @override
   State<StatefulWidget> createState() => BadWidgetState();
 }

packages/flutter/test/widgets/shader_mask_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' show Shader;
 
 import 'package:flutter_test/flutter_test.dart';
@@ -26,7 +24,7 @@ void main() {
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/44152
 
   testWidgets('Bounds rect includes offset', (WidgetTester tester) async {
-    Rect shaderBounds;
+    late Rect shaderBounds;
     Shader recordShaderBounds(Rect bounds) {
       shaderBounds = bounds;
       return createShader(bounds);

packages/flutter/test/widgets/shadow_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';
 
@@ -79,7 +77,7 @@ void main() {
             color: Colors.yellow[200],
             child: PhysicalModel(
               elevation: 9.0,
-              color: Colors.blue[900],
+              color: Colors.blue[900]!,
               child: const SizedBox(
                 height: 100.0,
                 width: 100.0,
@@ -111,7 +109,7 @@ void main() {
             padding: const EdgeInsets.all(150.0),
             color: Colors.yellow[200],
             child: PhysicalShape(
-              color: Colors.green[900],
+              color: Colors.green[900]!,
               clipper: ShapeBorderClipper(shape: BeveledRectangleBorder(
                 borderRadius: BorderRadius.circular(20.0))),
               elevation: elevation,

packages/flutter/test/widgets/shape_decoration_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' as ui show Image;
 

packages/flutter/test/widgets/shortcuts_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/services.dart';
@@ -11,11 +9,11 @@ import 'package:flutter/src/services/keyboard_key.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-typedef PostInvokeCallback = void Function({Action<Intent> action, Intent intent, BuildContext context, ActionDispatcher dispatcher});
+typedef PostInvokeCallback = void Function({Action<Intent> action, Intent intent, BuildContext? context, ActionDispatcher dispatcher});
 
 class TestAction extends CallbackAction<TestIntent> {
   TestAction({
-    @required OnInvokeCallback onInvoke,
+    required OnInvokeCallback onInvoke,
   })  : assert(onInvoke != null),
         super(onInvoke: onInvoke);
 
@@ -25,11 +23,11 @@ class TestAction extends CallbackAction<TestIntent> {
 class TestDispatcher extends ActionDispatcher {
   const TestDispatcher({this.postInvoke});
 
-  final PostInvokeCallback postInvoke;
+  final PostInvokeCallback? postInvoke;
 
   @override
-  Object invokeAction(Action<TestIntent> action, Intent intent, [BuildContext context]) {
-    final Object result = super.invokeAction(action, intent, context);
+  Object? invokeAction(Action<TestIntent> action, Intent intent, [BuildContext? context]) {
+    final Object? result = super.invokeAction(action, intent, context);
     postInvoke?.call(action: action, intent: intent, context: context, dispatcher: this);
     return result;
   }
@@ -45,7 +43,7 @@ class TestShortcutManager extends ShortcutManager {
   List<LogicalKeyboardKey> keys;
 
   @override
-  bool handleKeypress(BuildContext context, RawKeyEvent event, {LogicalKeySet keysPressed}) {
+  bool handleKeypress(BuildContext context, RawKeyEvent event, {LogicalKeySet? keysPressed}) {
     keys.add(event.logicalKey);
     return super.handleKeypress(context, event, keysPressed: keysPressed);
   }
@@ -239,7 +237,7 @@ void main() {
         ),
       );
       await tester.pump();
-      expect(Shortcuts.of(containerKey.currentContext), isNotNull);
+      expect(Shortcuts.of(containerKey.currentContext!), isNotNull);
       await tester.sendKeyDownEvent(LogicalKeyboardKey.shiftLeft);
       expect(invoked, isTrue);
       expect(pressedKeys, equals(<LogicalKeyboardKey>[LogicalKeyboardKey.shiftLeft]));
@@ -277,7 +275,7 @@ void main() {
         ),
       );
       await tester.pump();
-      expect(Shortcuts.of(containerKey.currentContext), isNotNull);
+      expect(Shortcuts.of(containerKey.currentContext!), isNotNull);
       await tester.sendKeyDownEvent(LogicalKeyboardKey.shiftLeft);
       expect(invoked, isTrue);
       expect(pressedKeys, equals(<LogicalKeyboardKey>[LogicalKeyboardKey.shiftLeft]));
@@ -317,7 +315,7 @@ void main() {
         ),
       );
       await tester.pump();
-      expect(Shortcuts.of(containerKey.currentContext), isNotNull);
+      expect(Shortcuts.of(containerKey.currentContext!), isNotNull);
       await tester.sendKeyDownEvent(LogicalKeyboardKey.shiftLeft);
       expect(invoked, isFalse);
       expect(pressedKeys, isEmpty);

packages/flutter/test/widgets/shrink_wrapping_viewport_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';

packages/flutter/test/widgets/simple_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 'dart:ui';
 
 import 'package:flutter/material.dart';

packages/flutter/test/widgets/single_child_scroll_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
-
 import 'dart:ui';
 
 import 'package:flutter_test/flutter_test.dart';
@@ -15,10 +13,10 @@ import 'semantics_tester.dart';
 
 class TestScrollPosition extends ScrollPositionWithSingleContext {
   TestScrollPosition({
-    ScrollPhysics physics,
-    ScrollContext state,
+    required ScrollPhysics physics,
+    required ScrollContext state,
     double initialPixels = 0.0,
-    ScrollPosition oldPosition,
+    ScrollPosition? oldPosition,
   }) : super(
     physics: physics,
     context: state,
@@ -29,7 +27,7 @@ class TestScrollPosition extends ScrollPositionWithSingleContext {
 
 class TestScrollController extends ScrollController {
   @override
-  ScrollPosition createScrollPosition(ScrollPhysics physics, ScrollContext context, ScrollPosition oldPosition) {
+  ScrollPosition createScrollPosition(ScrollPhysics physics, ScrollContext context, ScrollPosition? oldPosition) {
     return TestScrollPosition(
       physics: physics,
       state: context,
@@ -53,7 +51,7 @@ void main() {
     );
 
     // 1st, check that the render object has received the default clip behavior.
-    final dynamic renderObject = tester.allRenderObjects.where((RenderObject o) => o.runtimeType.toString() == '_RenderSingleChildViewport').first;
+    final dynamic renderObject = tester.allRenderObjects.where((RenderObject o) => o.runtimeType.toString() == '_RenderSingleChildViewport').first; // ignore: unnecessary_nullable_for_final_variable_declarations
     expect(renderObject.clipBehavior, equals(Clip.hardEdge));
 
     // 2nd, height == widow.height test: check that the painting context does not call pushClipRect .
@@ -107,7 +105,7 @@ void main() {
     await tester.pumpWidget(SingleChildScrollView(child: Container(height: 2000.0)));
 
     // 1st, check that the render object has received the default clip behavior.
-    final dynamic renderObject = tester.allRenderObjects.where((RenderObject o) => o.runtimeType.toString() == '_RenderSingleChildViewport').first;
+    final dynamic renderObject = tester.allRenderObjects.where((RenderObject o) => o.runtimeType.toString() == '_RenderSingleChildViewport').first; // ignore: unnecessary_nullable_for_final_variable_declarations
     expect(renderObject.clipBehavior, equals(Clip.hardEdge));
 
     // 2nd, check that the painting context has received the default clip behavior.
@@ -630,7 +628,15 @@ void main() {
   });
 
   testWidgets('Nested SingleChildScrollView showOnScreen', (WidgetTester tester) async {
-    final List<List<Widget>> children = List<List<Widget>>(10);
+    final List<List<Widget>> children = List<List<Widget>>.generate(10, (int x) {
+      return List<Widget>.generate(10, (int y) {
+        return SizedBox(
+          key: UniqueKey(),
+          height: 100.0,
+          width: 100.0,
+        );
+      });
+    });
     ScrollController controllerX;
     ScrollController controllerY;
 
@@ -665,17 +671,11 @@ void main() {
                 controller: controllerX = ScrollController(initialScrollOffset: 400.0),
                 scrollDirection: Axis.horizontal,
                 child: Column(
-                  children: List<Widget>.generate(10, (int y) {
+                  children: children.map((List<Widget> widgets) {
                     return Row(
-                      children: children[y] = List<Widget>.generate(10, (int x) {
-                        return SizedBox(
-                          key: UniqueKey(),
-                          height: 100.0,
-                          width: 100.0,
-                        );
-                      }),
+                      children: widgets,
                     );
-                  }),
+                  }).toList(),
                 ),
               ),
             ),
@@ -792,9 +792,9 @@ void main() {
   });
 
   group('Nested SingleChildScrollView (same orientation) showOnScreen', () {
-    List<Widget> children;
+    late List<Widget> children;
 
-    Future<void> buildNestedScroller({ WidgetTester tester, ScrollController inner, ScrollController outer }) {
+    Future<void> buildNestedScroller({ required WidgetTester tester, ScrollController? inner, ScrollController? outer }) {
       return tester.pumpWidget(
         Directionality(
           textDirection: TextDirection.ltr,

packages/flutter/test/widgets/size_changed_layout_notification_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/sized_box_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';
 
@@ -48,7 +46,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+    expect(patient.currentContext!.size, equals(const Size(0.0, 0.0)));
 
     await tester.pumpWidget(
       Center(
@@ -58,7 +56,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+    expect(patient.currentContext!.size, equals(const Size(0.0, 0.0)));
 
     await tester.pumpWidget(
       Center(
@@ -69,7 +67,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+    expect(patient.currentContext!.size, equals(const Size(0.0, 0.0)));
 
     await tester.pumpWidget(
       Center(
@@ -80,7 +78,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(100.0, 100.0)));
+    expect(patient.currentContext!.size, equals(const Size(100.0, 100.0)));
 
     await tester.pumpWidget(
       Center(
@@ -91,7 +89,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+    expect(patient.currentContext!.size, equals(const Size(800.0, 600.0)));
 
     await tester.pumpWidget(
       Center(
@@ -100,7 +98,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+    expect(patient.currentContext!.size, equals(const Size(800.0, 600.0)));
 
     await tester.pumpWidget(
       Center(
@@ -109,7 +107,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+    expect(patient.currentContext!.size, equals(const Size(0.0, 0.0)));
   });
 
   testWidgets('SizedBox - container child', (WidgetTester tester) async {
@@ -123,7 +121,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+    expect(patient.currentContext!.size, equals(const Size(800.0, 600.0)));
 
     await tester.pumpWidget(
       Center(
@@ -134,7 +132,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(800.0, 0.0)));
+    expect(patient.currentContext!.size, equals(const Size(800.0, 0.0)));
 
     await tester.pumpWidget(
       Center(
@@ -146,7 +144,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+    expect(patient.currentContext!.size, equals(const Size(0.0, 0.0)));
 
     await tester.pumpWidget(
       Center(
@@ -158,7 +156,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(100.0, 100.0)));
+    expect(patient.currentContext!.size, equals(const Size(100.0, 100.0)));
 
     await tester.pumpWidget(
       Center(
@@ -170,7 +168,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+    expect(patient.currentContext!.size, equals(const Size(800.0, 600.0)));
 
     await tester.pumpWidget(
       Center(
@@ -180,7 +178,7 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(800.0, 600.0)));
+    expect(patient.currentContext!.size, equals(const Size(800.0, 600.0)));
 
     await tester.pumpWidget(
       Center(
@@ -190,6 +188,6 @@ void main() {
         ),
       ),
     );
-    expect(patient.currentContext.size, equals(const Size(0.0, 0.0)));
+    expect(patient.currentContext!.size, equals(const Size(0.0, 0.0)));
   });
 }

packages/flutter/test/widgets/sliver_appbar_opacity_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_test/flutter_test.dart';
 import 'package:flutter/material.dart';
@@ -21,11 +19,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 0.0);
+    expect(render.text.style!.color!.opacity, 0.0);
   });
 
   testWidgets('!pinned && !floating && bottom ==> fade opacity', (WidgetTester tester) async {
@@ -40,11 +38,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 0.0);
+    expect(render.text.style!.color!.opacity, 0.0);
   });
 
   testWidgets('!pinned && floating && !bottom ==> fade opacity', (WidgetTester tester) async {
@@ -59,11 +57,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 0.0);
+    expect(render.text.style!.color!.opacity, 0.0);
   });
 
   testWidgets('!pinned && floating && bottom ==> fade opacity', (WidgetTester tester) async {
@@ -78,11 +76,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 0.0);
+    expect(render.text.style!.color!.opacity, 0.0);
   });
 
   testWidgets('pinned && !floating && !bottom ==> 1.0 opacity', (WidgetTester tester) async {
@@ -97,11 +95,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
   });
 
   testWidgets('pinned && !floating && bottom ==> 1.0 opacity', (WidgetTester tester) async {
@@ -116,11 +114,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
   });
 
   testWidgets('pinned && floating && !bottom ==> 1.0 opacity', (WidgetTester tester) async {
@@ -137,11 +135,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
   });
 
   testWidgets('pinned && floating && bottom && extraToolbarHeight == 0.0 ==> fade opacity', (WidgetTester tester) async {
@@ -158,11 +156,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 0.0);
+    expect(render.text.style!.color!.opacity, 0.0);
   });
 
   testWidgets('pinned && floating && bottom && extraToolbarHeight != 0.0 ==> 1.0 opacity', (WidgetTester tester) async {
@@ -178,11 +176,11 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
   });
 
   testWidgets('!pinned && !floating && !bottom && extraToolbarHeight != 0.0 ==> fade opacity', (WidgetTester tester) async {
@@ -199,20 +197,20 @@ void main() {
     );
 
     final RenderParagraph render = tester.renderObject(find.text('Hallo Welt!!1'));
-    expect(render.text.style.color.opacity, 1.0);
+    expect(render.text.style!.color!.opacity, 1.0);
 
     controller.jumpTo(collapsedHeight);
     await tester.pumpAndSettle();
-    expect(render.text.style.color.opacity, 0.0);
+    expect(render.text.style!.color!.opacity, 0.0);
   });
 }
 
 class _TestWidget extends StatelessWidget {
 
   const _TestWidget({
-    this.pinned,
-    this.floating,
-    this.bottom,
+    required this.pinned,
+    required this.floating,
+    required this.bottom,
     this.controller,
     this.collapsedHeight,
   });
@@ -220,8 +218,8 @@ class _TestWidget extends StatelessWidget {
   final bool pinned;
   final bool floating;
   final bool bottom;
-  final ScrollController controller;
-  final double collapsedHeight;
+  final ScrollController? controller;
+  final double? collapsedHeight;
 
   @override
   Widget build(BuildContext context) {

packages/flutter/test/widgets/sliver_constraints_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/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -39,7 +37,7 @@ void main() {
     // can fit in the viewport, and the SliverList doesn't report a child count,
     // so the SliverList leads to an infinite precedingScrollExtent.
     final RenderViewport renderViewport = tester.renderObject(find.byType(Viewport));
-    final RenderSliver lastRenderSliver = renderViewport.lastChild;
+    final RenderSliver lastRenderSliver = renderViewport.lastChild!;
     expect(lastRenderSliver.constraints.precedingScrollExtent, double.infinity);
   });
 }

packages/flutter/test/widgets/sliver_fill_remaining_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';
 import 'package:flutter/material.dart';
@@ -21,7 +19,7 @@ void main() {
   );
   Widget boilerplate(
     List<Widget> slivers, {
-      ScrollController controller,
+      ScrollController? controller,
       Axis scrollDirection = Axis.vertical,
     }) {
     return MaterialApp(

packages/flutter/test/widgets/sliver_fill_viewport_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_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
@@ -174,7 +172,7 @@ void main() {
     );
 
     final RenderSliver boxWithPadding = tester.renderObject<RenderSliver>(find.byType(SliverFillViewport));
-    expect(boxWithPadding.geometry.paintExtent, equals(600.0));
+    expect(boxWithPadding.geometry!.paintExtent, equals(600.0));
 
     await tester.pumpWidget(
       Directionality(
@@ -192,6 +190,6 @@ void main() {
     );
 
     final RenderSliver boxWithoutPadding = tester.renderObject<RenderSliver>(find.byType(SliverFillViewport));
-    expect(boxWithoutPadding.geometry.paintExtent, equals(300.0));
+    expect(boxWithoutPadding.geometry!.paintExtent, equals(300.0));
   });
 }

packages/flutter/test/widgets/sliver_list_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/widgets.dart';
 import 'package:flutter/material.dart';
@@ -368,7 +366,7 @@ Widget _buildSliverListRenderWidgetChild(List<String> items) {
 
 Widget _buildSliverList({
   List<int> items = const <int>[],
-  ScrollController controller,
+  ScrollController? controller,
   double itemHeight = 500.0,
   double viewportHeight = 300.0,
 }) {

packages/flutter/test/widgets/sliver_prototype_item_extent_test.dart

@@ -2,16 +2,14 @@
 // 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';
 
 class TestItem extends StatelessWidget {
-  const TestItem({ Key key, this.item, this.width, this.height }) : super(key: key);
+  const TestItem({ Key? key, required this.item, this.width, this.height }) : super(key: key);
   final int item;
-  final double width;
-  final double height;
+  final double? width;
+  final double? height;
   @override
   Widget build(BuildContext context) {
     return Container(
@@ -23,7 +21,7 @@ class TestItem extends StatelessWidget {
   }
 }
 
-Widget buildFrame({ int count, double width, double height, Axis scrollDirection }) {
+Widget buildFrame({ int? count, double? width, double? height, Axis? scrollDirection }) {
   return Directionality(
     textDirection: TextDirection.ltr,
     child: CustomScrollView(

packages/flutter/test/widgets/sliver_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 'dart:ui';
 
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/widgets/slivers_appbar_floating_pinned_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_test/flutter_test.dart';
 import 'package:flutter/material.dart';
@@ -336,15 +334,15 @@ void main() {
     );
     final RenderSliverFloatingPinnedPersistentHeader render = tester.renderObject(find.byType(SliverAppBar));
     expect(render.minExtent, greaterThan(availableHeight)); // Precondition
-    expect(render.geometry.scrollExtent, 120.0);
-    expect(render.geometry.paintExtent, availableHeight);
-    expect(render.geometry.layoutExtent, availableHeight);
+    expect(render.geometry!.scrollExtent, 120.0);
+    expect(render.geometry!.paintExtent, availableHeight);
+    expect(render.geometry!.layoutExtent, availableHeight);
 
     controller.jumpTo(200.0);
     await tester.pumpAndSettle();
-    expect(render.geometry.scrollExtent, 120.0);
-    expect(render.geometry.paintExtent, availableHeight);
-    expect(render.geometry.layoutExtent, 0.0);
+    expect(render.geometry!.scrollExtent, 120.0);
+    expect(render.geometry!.paintExtent, availableHeight);
+    expect(render.geometry!.layoutExtent, 0.0);
   });
 
   testWidgets('Pinned and floating SliverAppBar sticks to top the content is scroll down', (WidgetTester tester) async {
@@ -378,7 +376,7 @@ void main() {
     await gesture.moveBy(const Offset(0, scrollDistance));
     await tester.pump();
 
-    expect(render.geometry.paintOrigin, -scrollDistance);
+    expect(render.geometry!.paintOrigin, -scrollDistance);
   });
 
   testWidgets('Floating SliverAppBar sticks to top the content is scroll down', (WidgetTester tester) async {
@@ -412,7 +410,7 @@ void main() {
     await gesture.moveBy(const Offset(0, scrollDistance));
     await tester.pump();
 
-    expect(render.geometry.paintOrigin, -scrollDistance);
+    expect(render.geometry!.paintOrigin, -scrollDistance);
   });
 
   testWidgets('Pinned SliverAppBar sticks to top the content is scroll down', (WidgetTester tester) async {
@@ -446,6 +444,6 @@ void main() {
     await gesture.moveBy(const Offset(0, scrollDistance));
     await tester.pump();
 
-    expect(render.geometry.paintOrigin, -scrollDistance);
+    expect(render.geometry!.paintOrigin, -scrollDistance);
   });
 }

packages/flutter/test/widgets/slivers_appbar_floating_test.dart

@@ -2,19 +2,17 @@
 // 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/rendering.dart';
 import 'package:flutter/widgets.dart';
 
 void verifyPaintPosition(GlobalKey key, Offset ideal, bool visible) {
-  final RenderSliver target = key.currentContext.findRenderObject() as RenderSliver;
+  final RenderSliver target = key.currentContext!.findRenderObject()! as RenderSliver;
   expect(target.parent, isA<RenderViewport>());
-  final SliverPhysicalParentData parentData = target.parentData as SliverPhysicalParentData;
+  final SliverPhysicalParentData parentData = target.parentData! as SliverPhysicalParentData;
   final Offset actual = parentData.paintOffset;
   expect(actual, ideal);
-  final SliverGeometry geometry = target.geometry;
+  final SliverGeometry geometry = target.geometry!;
   expect(geometry.visible, visible);
 }
 
@@ -259,7 +257,7 @@ class RenderBigSliver extends RenderSliver {
     markNeedsLayout();
   }
 
-  double get paintExtent => (height - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent) as double;
+  double get paintExtent => (height - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent);
 
   @override
   void performLayout() {
@@ -272,7 +270,7 @@ class RenderBigSliver extends RenderSliver {
 }
 
 class BigSliver extends LeafRenderObjectWidget {
-  const BigSliver({ Key key, this.height }) : super(key: key);
+  const BigSliver({ Key? key, required this.height }) : super(key: key);
 
   final double height;
 

packages/flutter/test/widgets/slivers_appbar_pinned_test.dart

@@ -2,19 +2,17 @@
 // 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/rendering.dart';
 import 'package:flutter/widgets.dart';
 
 void verifyPaintPosition(GlobalKey key, Offset ideal, bool visible) {
-  final RenderSliver target = key.currentContext.findRenderObject() as RenderSliver;
+  final RenderSliver target = key.currentContext!.findRenderObject()! as RenderSliver;
   expect(target.parent, isA<RenderViewport>());
-  final SliverPhysicalParentData parentData = target.parentData as SliverPhysicalParentData;
+  final SliverPhysicalParentData parentData = target.parentData! as SliverPhysicalParentData;
   final Offset actual = parentData.paintOffset;
   expect(actual, ideal);
-  final SliverGeometry geometry = target.geometry;
+  final SliverGeometry geometry = target.geometry!;
   expect(geometry.visible, visible);
 }
 
@@ -76,7 +74,7 @@ void main() {
     );
     await tester.pumpAndSettle(const Duration(milliseconds: 10));
 
-    final RenderObject renderObject = key.currentContext.findRenderObject();
+    final RenderObject renderObject = key.currentContext!.findRenderObject()!;
     // The delegate must only start throwing immediately before calling
     // toStringDeep to avoid triggering spurious exceptions.
     // If the _RenderSliverPinnedPersistentHeaderForWidgets class was not
@@ -348,7 +346,7 @@ class RenderBigSliver extends RenderSliver {
     markNeedsLayout();
   }
 
-  double get paintExtent => (height - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent) as double;
+  double get paintExtent => (height - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent);
 
   @override
   void performLayout() {
@@ -361,7 +359,7 @@ class RenderBigSliver extends RenderSliver {
 }
 
 class BigSliver extends LeafRenderObjectWidget {
-  const BigSliver({ Key key, this.height }) : super(key: key);
+  const BigSliver({ Key? key, required this.height }) : super(key: key);
 
   final double height;
 

packages/flutter/test/widgets/slivers_appbar_scrolling_test.dart

@@ -2,16 +2,14 @@
 // 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/rendering.dart';
 import 'package:flutter/widgets.dart';
 
 void verifyPaintPosition(GlobalKey key, Offset ideal) {
-  final RenderObject target = key.currentContext.findRenderObject();
+  final RenderObject target = key.currentContext!.findRenderObject()!;
   expect(target.parent, isA<RenderViewport>());
-  final SliverPhysicalParentData parentData = target.parentData as SliverPhysicalParentData;
+  final SliverPhysicalParentData parentData = target.parentData! as SliverPhysicalParentData;
   final Offset actual = parentData.paintOffset;
   expect(actual, ideal);
 }
@@ -160,7 +158,7 @@ class TestDelegate extends SliverPersistentHeaderDelegate {
 
 class RenderBigSliver extends RenderSliver {
   static const double height = 550.0;
-  double get paintExtent => (height - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent) as double;
+  double get paintExtent => (height - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent);
 
   @override
   void performLayout() {
@@ -173,7 +171,7 @@ class RenderBigSliver extends RenderSliver {
 }
 
 class BigSliver extends LeafRenderObjectWidget {
-  const BigSliver({ Key key }) : super(key: key);
+  const BigSliver({ Key? key }) : super(key: key);
   @override
   RenderBigSliver createRenderObject(BuildContext context) {
     return RenderBigSliver();

packages/flutter/test/widgets/slivers_appbar_stretch_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/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -41,9 +39,9 @@ void main() {
       final RenderSliverScrollingPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100));
-      expect(header.child.size.height, equals(200.0));
+      expect(header.child!.size.height, equals(200.0));
     });
 
     testWidgets('does not stretch without overscroll physics', (WidgetTester tester) async {
@@ -76,9 +74,9 @@ void main() {
       final RenderSliverScrollingPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100.0));
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
     });
 
     testWidgets('default trigger offset', (WidgetTester tester) async {
@@ -92,9 +90,8 @@ void main() {
               SliverAppBar(
                 stretch: true,
                 expandedHeight: 100.0,
-                onStretchTrigger: () {
+                onStretchTrigger: () async {
                   didTrigger = true;
-                  return;
                 },
               ),
               SliverToBoxAdapter(
@@ -132,9 +129,8 @@ void main() {
                 stretch: true,
                 expandedHeight: 100.0,
                 stretchTriggerOffset: 150.0,
-                onStretchTrigger: () {
+                onStretchTrigger: () async {
                   didTrigger = true;
-                  return;
                 },
               ),
               SliverToBoxAdapter(
@@ -172,9 +168,8 @@ void main() {
                 stretch: true,
                 expandedHeight: 100.0,
                 stretchTriggerOffset: 150.0,
-                onStretchTrigger: () {
+                onStretchTrigger: () async {
                   didTrigger = true;
-                  return;
                 },
               ),
               SliverToBoxAdapter(
@@ -200,35 +195,6 @@ void main() {
       expect(didTrigger, isFalse);
     });
 
-    testWidgets('asserts stretch != null', (WidgetTester tester) async {
-      expect(
-        () {
-          return MaterialApp(
-            home: CustomScrollView(
-              physics: const ClampingScrollPhysics(),
-              slivers: <Widget>[
-                SliverAppBar(
-                  stretch: null,
-                  expandedHeight: 100.0,
-                ),
-                SliverToBoxAdapter(
-                  child: Container(
-                    height: 800,
-                  )
-                ),
-                SliverToBoxAdapter(
-                  child: Container(
-                    height: 800,
-                  )
-                ),
-              ],
-            ),
-          );
-        },
-        throwsAssertionError,
-      );
-    });
-
     testWidgets('asserts reasonable trigger offset', (WidgetTester tester) async {
       expect(
         () {
@@ -291,9 +257,9 @@ void main() {
       final RenderSliverPinnedPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100));
-      expect(header.child.size.height, equals(200.0));
+      expect(header.child!.size.height, equals(200.0));
     });
 
     testWidgets('does not stretch without overscroll physics', (WidgetTester tester) async {
@@ -326,9 +292,9 @@ void main() {
       final RenderSliverPinnedPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100));
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
     });
   });
 
@@ -363,9 +329,9 @@ void main() {
       final RenderSliverFloatingPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100));
-      expect(header.child.size.height, equals(200.0));
+      expect(header.child!.size.height, equals(200.0));
     });
 
     testWidgets('does not fill overscroll without proper physics', (WidgetTester tester) async {
@@ -398,9 +364,9 @@ void main() {
       final RenderSliverFloatingPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100));
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
     });
   });
 
@@ -436,9 +402,9 @@ void main() {
       final RenderSliverFloatingPinnedPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100));
-      expect(header.child.size.height, equals(200.0));
+      expect(header.child!.size.height, equals(200.0));
     });
 
     testWidgets('does not fill overscroll without proper physics', (WidgetTester tester) async {
@@ -472,9 +438,9 @@ void main() {
       final RenderSliverFloatingPinnedPersistentHeader header = tester.renderObject(
         find.byType(SliverAppBar)
       );
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
       await slowDrag(tester, anchor, const Offset(0.0, 100));
-      expect(header.child.size.height, equals(100.0));
+      expect(header.child!.size.height, equals(100.0));
     });
   });
 }

packages/flutter/test/widgets/slivers_block_global_key_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/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -11,7 +9,7 @@ import 'package:flutter/widgets.dart';
 int globalGeneration = 0;
 
 class GenerationText extends StatefulWidget {
-  const GenerationText(this.value, { Key key }) : super(key: key);
+  const GenerationText(this.value, { Key? key }) : super(key: key);
   final int value;
   @override
   _GenerationTextState createState() => _GenerationTextState();
@@ -55,7 +53,7 @@ void verify(WidgetTester tester, List<Offset> answerKey, String text) {
   expect(testAnswers, equals(answerKey));
   final String foundText =
     tester.widgetList<Text>(find.byType(Text))
-        .map<String>((Text widget) => widget.data)
+        .map<String>((Text widget) => widget.data!)
         .reduce((String value, String element) => value + element);
   expect(foundText, equals(text));
 }

packages/flutter/test/widgets/slivers_block_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/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -61,7 +59,7 @@ void verify(WidgetTester tester, List<Offset> answerKey, String text) {
   expect(testAnswers, equals(answerKey));
   final String foundText =
     tester.widgetList<Text>(find.byType(Text))
-    .map<String>((Text widget) => widget.data)
+    .map<String>((Text widget) => widget.data!)
     .reduce((String value, String element) => value + element);
   expect(foundText, equals(text));
 }