[NNBD] Migrate some Widgets tests (#68157)

5aef988a · Kate Lovett · GitHub · 73301a35 · 5aef988a · 5aef988a
Unverified Commit 5aef988a authored Oct 15, 2020 by Kate Lovett Committed by GitHub Oct 15, 2020
27 changed files
--- a/packages/flutter/lib/src/services/platform_channel.dart
+++ b/packages/flutter/lib/src/services/platform_channel.dart
@@ -412,7 +412,7 @@ class MethodChannel {
  /// return value of the call. The value will be encoded using
  /// [MethodCodec.encodeSuccessEnvelope], to act as if platform plugin had
  /// returned that value.
-  void setMockMethodCallHandler(Future<dynamic> Function(MethodCall call)? handler) {
+  void setMockMethodCallHandler(Future<dynamic>? Function(MethodCall call)? handler) {
    _methodChannelMockHandlers[this] = handler;
    binaryMessenger.setMockMessageHandler(
      name,
@@ -430,7 +430,7 @@ class MethodChannel {
  /// is not set.
  bool checkMockMethodCallHandler(Future<dynamic> Function(MethodCall call)? handler) => _methodChannelMockHandlers[this] == handler;
-  Future<ByteData?> _handleAsMethodCall(ByteData? message, Future<dynamic> handler(MethodCall call)) async {
+  Future<ByteData?> _handleAsMethodCall(ByteData? message, Future<dynamic>? handler(MethodCall call)) async {
    final MethodCall call = codec.decodeMethodCall(message);
    try {
      return codec.encodeSuccessEnvelope(await handler(call));

--- a/packages/flutter/test/services/autofill_test.dart
+++ b/packages/flutter/test/services/autofill_test.dart
@@ -195,7 +195,7 @@ class FakeTextChannel implements MethodChannel {
  bool checkMethodCallHandler(Future<void> Function(MethodCall call)? handler) => throw UnimplementedError();
  @override
-  void setMockMethodCallHandler(Future<void> Function(MethodCall call)? handler)  => throw UnimplementedError();
+  void setMockMethodCallHandler(Future<void>? Function(MethodCall call)? handler)  => throw UnimplementedError();
  @override
  bool checkMockMethodCallHandler(Future<void> Function(MethodCall call)? handler) => throw UnimplementedError();

--- a/packages/flutter/test/services/text_input_test.dart
+++ b/packages/flutter/test/services/text_input_test.dart
@@ -460,7 +460,7 @@ class FakeTextChannel implements MethodChannel {
  @override
-  void setMockMethodCallHandler(Future<void> Function(MethodCall call)? handler)  => throw UnimplementedError();
+  void setMockMethodCallHandler(Future<void>? Function(MethodCall call)? handler)  => throw UnimplementedError();
  @override
  bool checkMockMethodCallHandler(Future<void> Function(MethodCall call)? handler) => throw UnimplementedError();

--- a/packages/flutter/test/widgets/overflow_box_test.dart
+++ b/packages/flutter/test/widgets/overflow_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_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -27,7 +25,7 @@ void main() {
        ),
      ),
    ));
-    final RenderBox box = inner.currentContext.findRenderObject() as RenderBox;
+    final RenderBox box = inner.currentContext!.findRenderObject()! as RenderBox;
    expect(box.localToGlobal(Offset.zero), equals(const Offset(745.0, 565.0)));
    expect(box.size, equals(const Size(100.0, 50.0)));
  });
@@ -64,7 +62,7 @@ void main() {
        ),
      ),
    ));
-    final RenderBox box = inner.currentContext.findRenderObject() as RenderBox;
+    final RenderBox box = inner.currentContext!.findRenderObject()! as RenderBox;
    expect(box.size, equals(const Size(50.0, 50.0)));
    expect(
      box.localToGlobal(box.size.center(Offset.zero)),
@@ -87,7 +85,7 @@ void main() {
        ),
      ),
    ));
-    final RenderBox box = inner.currentContext.findRenderObject() as RenderBox;
+    final RenderBox box = inner.currentContext!.findRenderObject()! as RenderBox;
    expect(box.size, equals(const Size(50.0, 50.0)));
    expect(
      box.localToGlobal(box.size.center(Offset.zero)),

--- a/packages/flutter/test/widgets/overlay_test.dart
+++ b/packages/flutter/test/widgets/overlay_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_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
@@ -23,8 +21,7 @@ void main() {
            OverlayEntry(
              builder: (BuildContext context) {
                didBuild = true;
-                final Overlay overlay = context.findAncestorWidgetOfExactType<Overlay>();
+                final Overlay overlay = context.findAncestorWidgetOfExactType<Overlay>()!;
-                expect(overlay, isNotNull);
                expect(overlay.key, equals(overlayKey));
                return Container();
              },
@@ -37,7 +34,7 @@ void main() {
      ),
    );
    expect(didBuild, isTrue);
-    final RenderObject theater = overlayKey.currentContext.findRenderObject();
+    final RenderObject theater = overlayKey.currentContext!.findRenderObject()!;
    expect(theater, hasAGoodToStringDeep);
    expect(
@@ -110,7 +107,7 @@ void main() {
        ),
      ),
    );
-    final RenderObject theater = overlayKey.currentContext.findRenderObject();
+    final RenderObject theater = overlayKey.currentContext!.findRenderObject()!;
    expect(theater, hasAGoodToStringDeep);
    expect(
@@ -189,7 +186,7 @@ void main() {
    expect(buildOrder, <String>['Base']);
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.insert(
      OverlayEntry(
        builder: (BuildContext context) {
@@ -227,7 +224,7 @@ void main() {
    expect(buildOrder, <String>['Base']);
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.insert(
      OverlayEntry(
          builder: (BuildContext context) {
@@ -272,7 +269,7 @@ void main() {
    expect(buildOrder, <String>['Base', 'Top']);
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.insert(
      OverlayEntry(
          builder: (BuildContext context) {
@@ -325,7 +322,7 @@ void main() {
    ];
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.insertAll(entries);
    await tester.pump();
@@ -371,7 +368,7 @@ void main() {
    ];
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.insertAll(entries, below: base);
    await tester.pump();
@@ -423,7 +420,7 @@ void main() {
    ];
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.insertAll(entries, above: base);
    await tester.pump();
@@ -486,7 +483,7 @@ void main() {
    ];
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.rearrange(rearranged);
    await tester.pump();
@@ -549,7 +546,7 @@ void main() {
    ];
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.rearrange(rearranged, above: initialEntries[2]);
    await tester.pump();
@@ -612,7 +609,7 @@ void main() {
    ];
    buildOrder.clear();
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    overlay.rearrange(rearranged, below: initialEntries[2]);
    await tester.pump();
@@ -639,7 +636,7 @@ void main() {
      ),
    );
-    final OverlayState overlay = overlayKey.currentState as OverlayState;
+    final OverlayState overlay = overlayKey.currentState! as OverlayState;
    try {
      overlay.insert(
@@ -657,8 +654,7 @@ void main() {
          },
        ),
      );
-    } catch (e) {
+    } on AssertionError catch (e) {
-      expect(e, isAssertionError);
      expect(e.message, 'Only one of `above` and `below` may be specified.');
    }
@@ -680,8 +676,7 @@ void main() {
          },
        ),
      );
-    } catch (e) {
+    } on AssertionError catch (e) {
-      expect(e, isAssertionError);
      expect(e.message, 'The provided entry used for `above` must be present in the Overlay.');
    }
@@ -692,8 +687,7 @@ void main() {
        },
      ));
-    } catch (e) {
+    } on AssertionError catch (e) {
-      expect(e, isAssertionError);
      expect(e.message, 'The provided entry used for `above` must be present in the Overlay and in the `newEntriesList`.');
    }
@@ -706,7 +700,7 @@ void main() {
        textDirection: TextDirection.ltr,
        child: Builder(
          builder: (BuildContext context) {
-            FlutterError error;
+            late FlutterError error;
            final Widget debugRequiredFor = Container();
            try {
              Overlay.of(context, debugRequiredFor: debugRequiredFor);
@@ -778,7 +772,7 @@ void main() {
    expect(newEntry.opaque, isTrue);
    // The new opaqueness is honored when inserted into an overlay.
-    overlayKey.currentState.insert(newEntry);
+    overlayKey.currentState!.insert(newEntry);
    await tester.pumpAndSettle();
    expect(find.byKey(root), findsNothing);
@@ -892,7 +886,7 @@ void main() {
    expect(tester.state<StatefulTestState>(find.byKey(bottom)).rebuildCount, 1);
    expect(tester.state<StatefulTestState>(find.byKey(top)).rebuildCount, 1);
-    overlayKey.currentState.rearrange(<OverlayEntry>[
+    overlayKey.currentState!.rearrange(<OverlayEntry>[
      bottomEntry, middleEntry, topEntry,
    ]);
    await tester.pump();
@@ -932,7 +926,7 @@ void main() {
    await tester.tap(find.byKey(overlayKey));
    expect(bottomTapCount, 1);
-    overlayKey.currentState.insert(OverlayEntry(
+    overlayKey.currentState!.insert(OverlayEntry(
      maintainState: true,
      opaque: true,
      builder: (BuildContext context) {
@@ -948,7 +942,7 @@ void main() {
    expect(bottomTapCount, 1);
    int topTapCount = 0;
-    overlayKey.currentState.insert(OverlayEntry(
+    overlayKey.currentState!.insert(OverlayEntry(
      maintainState: true,
      opaque: true,
      builder: (BuildContext context) {
@@ -1026,6 +1020,7 @@ void main() {
  });
  testWidgets('Overlay can set and update clipBehavior', (WidgetTester tester) async {
    await tester.pumpWidget(
      Directionality(
        textDirection: TextDirection.ltr,
@@ -1040,6 +1035,7 @@ void main() {
    );
    // By default, clipBehavior should be Clip.hardEdge
+    // ignore: unnecessary_nullable_for_final_variable_declarations
    final dynamic renderObject = tester.renderObject(find.byType(Overlay));
    expect(renderObject.clipBehavior, equals(Clip.hardEdge));
@@ -1063,7 +1059,7 @@ void main() {
 }
 class StatefulTestWidget extends StatefulWidget {
-  const StatefulTestWidget({Key key}) : super(key: key);
+  const StatefulTestWidget({Key? key}) : super(key: key);
  @override
  State<StatefulTestWidget> createState() => StatefulTestState();

--- a/packages/flutter/test/widgets/overscroll_indicator_test.dart
+++ b/packages/flutter/test/widgets/overscroll_indicator_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' as math;
 import 'package:flutter_test/flutter_test.dart';

--- a/packages/flutter/test/widgets/page_forward_transitions_test.dart
+++ b/packages/flutter/test/widgets/page_forward_transitions_test.dart
@@ -2,18 +2,16 @@
 // 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';
 class TestTransition extends AnimatedWidget {
  const TestTransition({
-    Key key,
+    Key? key,
-    this.childFirstHalf,
+    required this.childFirstHalf,
-    this.childSecondHalf,
+    required this.childSecondHalf,
-    Animation<double> animation,
+    required Animation<double> animation,
  }) : super(key: key, listenable: animation);
  final Widget childFirstHalf;
@@ -29,7 +27,11 @@ class TestTransition extends AnimatedWidget {
 }
 class TestRoute<T> extends PageRoute<T> {
-  TestRoute({ this.child, RouteSettings settings, this.barrierColor }) : super(settings: settings);
+  TestRoute({
+    required this.child,
+    required RouteSettings settings,
+    this.barrierColor,
+  }) : super(settings: settings);
  final Widget child;
@@ -37,10 +39,10 @@ class TestRoute<T> extends PageRoute<T> {
  Duration get transitionDuration => const Duration(milliseconds: 150);
  @override
-  final Color barrierColor;
+  final Color? barrierColor;
  @override
-  String get barrierLabel => null;
+  String? get barrierLabel => null;
  @override
  bool get maintainState => false;
@@ -88,18 +90,18 @@ void main() {
                child: Builder(
                  key: insideKey,
                  builder: (BuildContext context) {
-                    final PageRoute<void> route = ModalRoute.of(context) as PageRoute<void>;
+                    final PageRoute<void> route = ModalRoute.of(context)! as PageRoute<void>;
                    return Column(
                      children: <Widget>[
                        TestTransition(
                          childFirstHalf: const Text('A'),
                          childSecondHalf: const Text('B'),
-                          animation: route.animation,
+                          animation: route.animation!,
                        ),
                        TestTransition(
                          childFirstHalf: const Text('C'),
                          childSecondHalf: const Text('D'),
-                          animation: route.secondaryAnimation,
+                          animation: route.secondaryAnimation!,
                        ),
                      ],
                    );
@@ -115,7 +117,7 @@ void main() {
      )
    );
-    final NavigatorState navigator = insideKey.currentContext.findAncestorStateOfType<NavigatorState>();
+    final NavigatorState navigator = insideKey.currentContext!.findAncestorStateOfType<NavigatorState>()!;
    expect(state(), equals('BC')); // transition ->1 is at 1.0

--- a/packages/flutter/test/widgets/page_route_builder_test.dart
+++ b/packages/flutter/test/widgets/page_route_builder_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_test/flutter_test.dart';
@@ -28,7 +26,7 @@ class HomePage extends StatefulWidget {
 class _HomePageState extends State<HomePage> {
  void _presentModalPage() {
-    Navigator.of(context).push(PageRouteBuilder<void>(
+    Navigator.of(context)!.push(PageRouteBuilder<void>(
      transitionDuration: const Duration(milliseconds: 300),
      barrierColor: Colors.black54,
      opaque: false,
@@ -64,7 +62,7 @@ class ModalPage extends StatelessWidget {
              highlightColor: Colors.transparent,
              splashColor: Colors.transparent,
              onTap: () {
-                Navigator.of(context).pop();
+                Navigator.of(context)!.pop();
              },
              child: const SizedBox.expand(),
            ),

--- a/packages/flutter/test/widgets/page_storage_test.dart
+++ b/packages/flutter/test/widgets/page_storage_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';
 void main() {
  testWidgets('PageStorage read and write', (WidgetTester tester) async {
    const Key builderKey = PageStorageKey<String>('builderKey');
-    StateSetter setState;
+    late StateSetter setState;
    int storedValue = 0;
    await tester.pumpWidget(
@@ -18,7 +16,7 @@ void main() {
        home: StatefulBuilder(
          key: builderKey,
          builder: (BuildContext context, StateSetter setter) {
-            PageStorage.of(context).writeState(context, storedValue);
+            PageStorage.of(context)!.writeState(context, storedValue);
            setState = setter;
            return Center(
              child: Text('storedValue: $storedValue'),
@@ -30,17 +28,17 @@ void main() {
    final Element builderElement = tester.element(find.byKey(builderKey));
    expect(PageStorage.of(builderElement), isNotNull);
-    expect(PageStorage.of(builderElement).readState(builderElement), equals(storedValue));
+    expect(PageStorage.of(builderElement)!.readState(builderElement), equals(storedValue));
    setState(() {
      storedValue = 1;
    });
    await tester.pump();
-    expect(PageStorage.of(builderElement).readState(builderElement), equals(storedValue));
+    expect(PageStorage.of(builderElement)!.readState(builderElement), equals(storedValue));
  });
  testWidgets('PageStorage read and write by identifier', (WidgetTester tester) async {
-    StateSetter setState;
+    late StateSetter setState;
    int storedValue = 0;
    Widget buildWidthKey(Key key) {
@@ -48,7 +46,7 @@ void main() {
        home: StatefulBuilder(
          key: key,
          builder: (BuildContext context, StateSetter setter) {
-            PageStorage.of(context).writeState(context, storedValue, identifier: 123);
+            PageStorage.of(context)!.writeState(context, storedValue, identifier: 123);
            setState = setter;
            return Center(
              child: Text('storedValue: $storedValue'),
@@ -62,8 +60,8 @@ void main() {
    await tester.pumpWidget(buildWidthKey(key));
    Element builderElement = tester.element(find.byKey(key));
    expect(PageStorage.of(builderElement), isNotNull);
-    expect(PageStorage.of(builderElement).readState(builderElement), isNull);
+    expect(PageStorage.of(builderElement)!.readState(builderElement), isNull);
-    expect(PageStorage.of(builderElement).readState(builderElement, identifier: 123), equals(storedValue));
+    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));
    // New StatefulBuilder widget - different key - but the same PageStorage identifier.
@@ -71,14 +69,14 @@ void main() {
    await tester.pumpWidget(buildWidthKey(key));
    builderElement = tester.element(find.byKey(key));
    expect(PageStorage.of(builderElement), isNotNull);
-    expect(PageStorage.of(builderElement).readState(builderElement), isNull);
+    expect(PageStorage.of(builderElement)!.readState(builderElement), isNull);
-    expect(PageStorage.of(builderElement).readState(builderElement, identifier: 123), equals(storedValue));
+    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));
    setState(() {
      storedValue = 1;
    });
    await tester.pump();
-    expect(PageStorage.of(builderElement).readState(builderElement, identifier: 123), equals(storedValue));
+    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));
  });
 }
--- a/packages/flutter/test/widgets/page_transitions_test.dart
+++ b/packages/flutter/test/widgets/page_transitions_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/material.dart';
 class TestOverlayRoute extends OverlayRoute<void> {
-  TestOverlayRoute({ RouteSettings settings }) : super(settings: settings);
+  TestOverlayRoute({ RouteSettings? settings }) : super(settings: settings);
  @override
  Iterable<OverlayEntry> createOverlayEntries() sync* {
    yield OverlayEntry(builder: _build);
@@ -17,7 +15,7 @@ class TestOverlayRoute extends OverlayRoute<void> {
 }
 class PersistentBottomSheetTest extends StatefulWidget {
-  const PersistentBottomSheetTest({ Key key }) : super(key: key);
+  const PersistentBottomSheetTest({ Key? key }) : super(key: key);
  @override
  PersistentBottomSheetTestState createState() => PersistentBottomSheetTestState();
@@ -29,7 +27,7 @@ class PersistentBottomSheetTestState extends State<PersistentBottomSheetTest> {
  bool setStateCalled = false;
  void showBottomSheet() {
-    _scaffoldKey.currentState.showBottomSheet<void>((BuildContext context) {
+    _scaffoldKey.currentState!.showBottomSheet<void>((BuildContext context) {
      return const Text('bottomSheet');
    })
    .closed.whenComplete(() {
@@ -63,9 +61,9 @@ void main() {
    expect(find.text('Settings'), findsNothing);
    expect(find.text('Overlay'), findsNothing);
-    expect(Navigator.canPop(containerKey1.currentContext), isFalse);
+    expect(Navigator.canPop(containerKey1.currentContext!), isFalse);
-    Navigator.pushNamed(containerKey1.currentContext, '/settings');
+    Navigator.pushNamed(containerKey1.currentContext!, '/settings');
-    expect(Navigator.canPop(containerKey1.currentContext), isTrue);
+    expect(Navigator.canPop(containerKey1.currentContext!), isTrue);
    await tester.pump();
@@ -85,7 +83,7 @@ void main() {
    expect(find.text('Settings'), isOnstage);
    expect(find.text('Overlay'), findsNothing);
-    Navigator.push(containerKey2.currentContext, TestOverlayRoute());
+    Navigator.push(containerKey2.currentContext!, TestOverlayRoute());
    await tester.pump();
@@ -99,8 +97,8 @@ void main() {
    expect(find.text('Settings'), isOnstage);
    expect(find.text('Overlay'), isOnstage);
-    expect(Navigator.canPop(containerKey2.currentContext), isTrue);
+    expect(Navigator.canPop(containerKey2.currentContext!), isTrue);
-    Navigator.pop(containerKey2.currentContext);
+    Navigator.pop(containerKey2.currentContext!);
    await tester.pump();
    expect(find.text('Home'), findsNothing);
@@ -113,8 +111,8 @@ void main() {
    expect(find.text('Settings'), isOnstage);
    expect(find.text('Overlay'), findsNothing);
-    expect(Navigator.canPop(containerKey2.currentContext), isTrue);
+    expect(Navigator.canPop(containerKey2.currentContext!), isTrue);
-    Navigator.pop(containerKey2.currentContext);
+    Navigator.pop(containerKey2.currentContext!);
    await tester.pump();
    await tester.pump();
@@ -128,7 +126,7 @@ void main() {
    expect(find.text('Settings'), findsNothing);
    expect(find.text('Overlay'), findsNothing);
-    expect(Navigator.canPop(containerKey1.currentContext), isFalse);
+    expect(Navigator.canPop(containerKey1.currentContext!), isFalse);
  });
  testWidgets('Check back gesture disables Heroes', (WidgetTester tester) async {
@@ -161,7 +159,7 @@ void main() {
    await tester.pumpWidget(MaterialApp(routes: routes));
-    Navigator.pushNamed(containerKey1.currentContext, '/settings');
+    Navigator.pushNamed(containerKey1.currentContext!, '/settings');
    await tester.pump();
    await tester.pump(const Duration(milliseconds: 16));
@@ -210,7 +208,7 @@ void main() {
    await tester.pumpWidget(MaterialApp(routes: routes));
-    Navigator.pushNamed(containerKey1.currentContext, '/settings');
+    Navigator.pushNamed(containerKey1.currentContext!, '/settings');
    await tester.pump();
    await tester.pump(const Duration(milliseconds: 100));
@@ -254,7 +252,7 @@ void main() {
    await tester.pumpWidget(MaterialApp(routes: routes));
-    Navigator.pushNamed(containerKey1.currentContext, '/sheet');
+    Navigator.pushNamed(containerKey1.currentContext!, '/sheet');
    await tester.pump();
    await tester.pump(const Duration(seconds: 1));
@@ -269,7 +267,7 @@ void main() {
    await tester.pump();
    await tester.pump(const Duration(seconds: 1));
-    Navigator.pushNamed(containerKey1.currentContext, '/sheet');
+    Navigator.pushNamed(containerKey1.currentContext!, '/sheet');
    await tester.pump();
    await tester.pump(const Duration(seconds: 1));
@@ -278,7 +276,7 @@ void main() {
    expect(find.text('Sheet'), isOnstage);
    // Show the bottom sheet.
-    final PersistentBottomSheetTestState sheet = containerKey2.currentState as PersistentBottomSheetTestState;
+    final PersistentBottomSheetTestState sheet = containerKey2.currentState! as PersistentBottomSheetTestState;
    sheet.showBottomSheet();
    await tester.pump(const Duration(seconds: 1));

--- a/packages/flutter/test/widgets/page_view_test.dart
+++ b/packages/flutter/test/widgets/page_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 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -333,7 +331,7 @@ void main() {
    final List<int> log = <int>[];
    final PageController controller = PageController(viewportFraction: 0.9);
-    Widget build(PageController controller, { Size size }) {
+    Widget build(PageController controller, { Size? size }) {
      final Widget pageView = Directionality(
        textDirection: TextDirection.ltr,
        child: PageView(
@@ -429,7 +427,7 @@ void main() {
  testWidgets('Page snapping disable and reenable', (WidgetTester tester) async {
    final List<int> log = <int>[];
-    Widget build({ bool pageSnapping }) {
+    Widget build({ required bool pageSnapping }) {
      return Directionality(
        textDirection: TextDirection.ltr,
        child: PageView(
@@ -643,7 +641,7 @@ void main() {
    (WidgetTester tester) async {
      // Regression test for https://github.com/flutter/flutter/issues/23873.
      final PageController controller = PageController(viewportFraction: 1/4, initialPage: 0);
-      int tappedIndex;
+      late int tappedIndex;
      Widget build() {
        return Directionality(

--- a/packages/flutter/test/widgets/pageable_list_test.dart
+++ b/packages/flutter/test/widgets/pageable_list_test.dart
@@ -2,17 +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';
-import 'package:meta/meta.dart';
 Size pageSize = const Size(600.0, 300.0);
 const List<int> defaultPages = <int>[0, 1, 2, 3, 4, 5];
 final List<GlobalKey> globalKeys = defaultPages.map<GlobalKey>((_) => GlobalKey()).toList();
-int currentPage;
+int? currentPage;
 Widget buildPage(int page) {
  return Container(
@@ -26,7 +23,7 @@ Widget buildPage(int page) {
 Widget buildFrame({
  bool reverse = false,
  List<int> pages = defaultPages,
-  @required TextDirection textDirection,
+  required TextDirection textDirection,
 }) {
  final PageView child = PageView(
    scrollDirection: Axis.horizontal,

--- a/packages/flutter/test/widgets/parent_data_test.dart
+++ b/packages/flutter/test/widgets/parent_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_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -13,10 +11,10 @@ import 'test_widgets.dart';
 class TestParentData {
  TestParentData({ this.top, this.right, this.bottom, this.left });
-  final double top;
+  final double? top;
-  final double right;
+  final double? right;
-  final double bottom;
+  final double? bottom;
-  final double left;
+  final double? left;
 }
 void checkTree(WidgetTester tester, List<TestParentData> expectedParentData) {
@@ -27,18 +25,18 @@ void checkTree(WidgetTester tester, List<TestParentData> expectedParentData) {
  expect(element.renderObject, isA<RenderStack>());
  final RenderStack renderObject = element.renderObject as RenderStack;
  try {
-    RenderObject child = renderObject.firstChild;
+    RenderObject? child = renderObject.firstChild;
    for (final TestParentData expected in expectedParentData) {
      expect(child, isA<RenderDecoratedBox>());
-      final RenderDecoratedBox decoratedBox = child as RenderDecoratedBox;
+      final RenderDecoratedBox decoratedBox = child! as RenderDecoratedBox;
      expect(decoratedBox.parentData, isA<StackParentData>());
-      final StackParentData parentData = decoratedBox.parentData as StackParentData;
+      final StackParentData parentData = decoratedBox.parentData! as StackParentData;
      expect(parentData.top, equals(expected.top));
      expect(parentData.right, equals(expected.right));
      expect(parentData.bottom, equals(expected.bottom));
      expect(parentData.left, equals(expected.left));
-      final StackParentData decoratedBoxParentData = decoratedBox.parentData as StackParentData;
+      final StackParentData? decoratedBoxParentData = decoratedBox.parentData as StackParentData?;
-      child = decoratedBoxParentData.nextSibling;
+      child = decoratedBoxParentData?.nextSibling;
    }
    expect(child, isNull);
  } catch (e) {
@@ -431,7 +429,7 @@ void main() {
        child: Container(),
      ),
    );
-    DummyParentData parentData = tester.renderObject(find.byType(Container)).parentData as DummyParentData;
+    DummyParentData parentData = tester.renderObject(find.byType(Container)).parentData! as DummyParentData;
    expect(parentData.string, isNull);
    await tester.pumpWidget(
@@ -442,7 +440,7 @@ void main() {
        ),
      ),
    );
-    parentData = tester.renderObject(find.byType(Container)).parentData as DummyParentData;
+    parentData = tester.renderObject(find.byType(Container)).parentData! as DummyParentData;
    expect(parentData.string, 'Foo');
    await tester.pumpWidget(
@@ -453,16 +451,16 @@ void main() {
        ),
      ),
    );
-    parentData = tester.renderObject(find.byType(Container)).parentData as DummyParentData;
+    parentData = tester.renderObject(find.byType(Container)).parentData! as DummyParentData;
    expect(parentData.string, 'Bar');
  });
 }
 class TestParentDataWidget extends ParentDataWidget<DummyParentData> {
  const TestParentDataWidget({
-    Key key,
+    Key? key,
-    this.string,
+    required this.string,
-    Widget child,
+    required Widget child,
  }) : super(key: key, child: child);
  final String string;
@@ -470,7 +468,7 @@ class TestParentDataWidget extends ParentDataWidget<DummyParentData> {
  @override
  void applyParentData(RenderObject renderObject) {
    assert(renderObject.parentData is DummyParentData);
-    final DummyParentData parentData = renderObject.parentData as DummyParentData;
+    final DummyParentData parentData = renderObject.parentData! as DummyParentData;
    parentData.string = string;
  }
@@ -479,13 +477,13 @@ class TestParentDataWidget extends ParentDataWidget<DummyParentData> {
 }
 class DummyParentData extends ParentData {
-  String string;
+  String? string;
 }
 class OneAncestorWidget extends SingleChildRenderObjectWidget {
  const OneAncestorWidget({
-    Key key,
+    Key? key,
-    Widget child,
+    required Widget child,
  }) : super(key: key, child: child);
  @override
@@ -494,8 +492,8 @@ class OneAncestorWidget extends SingleChildRenderObjectWidget {
 class AnotherAncestorWidget extends SingleChildRenderObjectWidget {
  const AnotherAncestorWidget({
-    Key key,
+    Key? key,
-    Widget child,
+    required Widget child,
  }) : super(key: key, child: child);
  @override

--- a/packages/flutter/test/widgets/performance_overlay_test.dart
+++ b/packages/flutter/test/widgets/performance_overlay_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';

--- a/packages/flutter/test/widgets/physical_model_test.dart
+++ b/packages/flutter/test/widgets/physical_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 'dart:math' as math show pi;
 import 'package:flutter/material.dart';
@@ -106,7 +104,7 @@ void main() {
    Future<void> _testStackChildren(
      WidgetTester tester,
      List<Widget> children, {
-      @required int expectedErrorCount,
+      required int expectedErrorCount,
      bool enableCheck = true,
    }) async {
      assert(expectedErrorCount != null);
@@ -117,7 +115,7 @@ void main() {
      }
      debugDisableShadows = false;
      int count = 0;
-      final void Function(FlutterErrorDetails) oldOnError = FlutterError.onError;
+      final void Function(FlutterErrorDetails)? oldOnError = FlutterError.onError;
      FlutterError.onError = (FlutterErrorDetails details) {
        count++;
      };

--- a/packages/flutter/test/widgets/placeholder_test.dart
+++ b/packages/flutter/test/widgets/placeholder_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';

--- a/packages/flutter/test/widgets/platform_view_test.dart
+++ b/packages/flutter/test/widgets/platform_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';
 import 'dart:typed_data';
@@ -65,7 +63,7 @@ void main() {
      );
      final FakeAndroidPlatformView fakeView = viewsController.views.first;
-      final Uint8List rawCreationParams = fakeView.creationParams;
+      final Uint8List rawCreationParams = fakeView.creationParams!;
      final ByteData byteData = ByteData.view(
          rawCreationParams.buffer,
          rawCreationParams.offsetInBytes,
@@ -141,7 +139,7 @@ void main() {
        ]),
      );
-      viewsController.resizeCompleter.complete();
+      viewsController.resizeCompleter!.complete();
      await tester.pump();
      expect(
@@ -946,7 +944,7 @@ void main() {
      expect(semantics.transform, Matrix4.translationValues(600, 500, 0));
      expect(semantics.childrenCount, 0);
-      viewsController.createCompleter.complete();
+      viewsController.createCompleter!.complete();
      await tester.pumpAndSettle();
      expect(semantics.platformViewId, currentViewId + 1);
@@ -992,8 +990,8 @@ void main() {
          ),
      );
      final Element containerElement = tester.element(find.byKey(containerKey));
-      final FocusNode androidViewFocusNode = androidViewFocusWidget.focusNode;
+      final FocusNode androidViewFocusNode = androidViewFocusWidget.focusNode!;
-      final FocusNode containerFocusNode = Focus.of(containerElement);
+      final FocusNode containerFocusNode = Focus.of(containerElement)!;
      containerFocusNode.requestFocus();
@@ -1036,16 +1034,16 @@ void main() {
        ),
      );
-      viewsController.createCompleter.complete();
+      viewsController.createCompleter!.complete();
      final Element containerElement = tester.element(find.byKey(containerKey));
-      final FocusNode containerFocusNode = Focus.of(containerElement);
+      final FocusNode containerFocusNode = Focus.of(containerElement)!;
      containerFocusNode.requestFocus();
      await tester.pump();
-      int lastPlatformViewTextClient;
+      late int lastPlatformViewTextClient;
      SystemChannels.textInput.setMockMethodCallHandler((MethodCall call) {
        if (call.method == 'TextInput.setPlatformViewClient') {
          lastPlatformViewTextClient = call.arguments as int;
@@ -1085,10 +1083,10 @@ void main() {
        ),
      );
-      viewsController.createCompleter.complete();
+      viewsController.createCompleter!.complete();
      final Element containerElement = tester.element(find.byKey(containerKey));
-      final FocusNode containerFocusNode = Focus.of(containerElement);
+      final FocusNode containerFocusNode = Focus.of(containerElement)!;
      containerFocusNode.requestFocus();
      await tester.pump();
@@ -1190,7 +1188,7 @@ void main() {
  });
  group('AndroidViewSurface', () {
-    FakeAndroidViewController controller;
+    late FakeAndroidViewController controller;
    setUp(() {
      controller = FakeAndroidViewController(0);
@@ -1314,7 +1312,7 @@ void main() {
        ),
      );
-      viewsController.creationDelay.complete();
+      viewsController.creationDelay!.complete();
      expect(
        viewsController.views,
@@ -1378,7 +1376,7 @@ void main() {
      );
      final FakeUiKitView fakeView = viewsController.views.first;
-      final Uint8List rawCreationParams = fakeView.creationParams;
+      final Uint8List rawCreationParams = fakeView.creationParams!;
      final ByteData byteData = ByteData.view(
          rawCreationParams.buffer,
          rawCreationParams.offsetInBytes,
@@ -1994,7 +1992,7 @@ void main() {
  });
  group('Common PlatformView', () {
-    FakePlatformViewController controller;
+    late FakePlatformViewController controller;
    setUp((){
      controller = FakePlatformViewController(0);
@@ -2257,9 +2255,9 @@ void main() {
    testWidgets('PlatformViewLink Widget init, should create a SizedBox widget before onPlatformViewCreated and a PlatformViewSurface after', (WidgetTester tester) async {
      final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
-      int createdPlatformViewId;
+      late int createdPlatformViewId;
-      PlatformViewCreatedCallback onPlatformViewCreatedCallBack;
+      late PlatformViewCreatedCallback onPlatformViewCreatedCallBack;
      final PlatformViewLink platformViewLink = PlatformViewLink(
        viewType: 'webview',
@@ -2289,7 +2287,7 @@ void main() {
    });
    testWidgets('PlatformViewLink Widget dispose', (WidgetTester tester) async {
-      FakePlatformViewController disposedController;
+      late FakePlatformViewController disposedController;
      final PlatformViewLink platformViewLink = PlatformViewLink(
        viewType: 'webview',
        onCreatePlatformView: (PlatformViewCreationParams params){
@@ -2454,8 +2452,8 @@ void main() {
    testWidgets('PlatformViewLink manages the focus properly', (WidgetTester tester) async {
      final GlobalKey containerKey = GlobalKey();
-      FakePlatformViewController controller;
+      late FakePlatformViewController controller;
-      ValueChanged<bool> focusChanged;
+      late ValueChanged<bool> focusChanged;
      final PlatformViewLink platformViewLink = PlatformViewLink(
        viewType: 'webview',
        onCreatePlatformView: (PlatformViewCreationParams params){
@@ -2491,9 +2489,9 @@ void main() {
              matching: find.byType(Focus),
          ),
      );
-      final FocusNode platformViewFocusNode = platformViewFocusWidget.focusNode;
+      final FocusNode platformViewFocusNode = platformViewFocusWidget.focusNode!;
      final Element containerElement = tester.element(find.byKey(containerKey));
-      final FocusNode containerFocusNode = Focus.of(containerElement);
+      final FocusNode containerFocusNode = Focus.of(containerElement)!;
      containerFocusNode.requestFocus();
      await tester.pump();

--- a/packages/flutter/test/widgets/positioned_test.dart
+++ b/packages/flutter/test/widgets/positioned_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 'package:flutter_test/flutter_test.dart';
@@ -78,8 +76,8 @@ void main() {
    final GlobalKey key = GlobalKey();
    void recordMetrics() {
-      final RenderBox box = key.currentContext.findRenderObject() as RenderBox;
+      final RenderBox box = key.currentContext!.findRenderObject()! as RenderBox;
-      final BoxParentData boxParentData = box.parentData as BoxParentData;
+      final BoxParentData boxParentData = box.parentData! as BoxParentData;
      sizes.add(box.size);
      positions.add(boxParentData.offset);
    }

--- a/packages/flutter/test/widgets/range_maintaining_scroll_physics_test.dart
+++ b/packages/flutter/test/widgets/range_maintaining_scroll_physics_test.dart
@@ -2,14 +2,12 @@
 // 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/gestures.dart';
 import 'package:flutter_test/flutter_test.dart';
 class ExpandingBox extends StatefulWidget {
-  const ExpandingBox({this.collapsedSize, this.expandedSize});
+  const ExpandingBox({ required this.collapsedSize, required this.expandedSize });
  final double collapsedSize;
  final double expandedSize;
@@ -19,7 +17,7 @@ class ExpandingBox extends StatefulWidget {
 }
 class _ExpandingBoxState extends State<ExpandingBox> with AutomaticKeepAliveClientMixin<ExpandingBox>{
-  double _height;
+  late double _height;
  @override
  void initState() {

--- a/packages/flutter/test/widgets/raw_keyboard_listener_test.dart
+++ b/packages/flutter/test/widgets/raw_keyboard_listener_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/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

--- a/packages/flutter/test/widgets/reassemble_test.dart
+++ b/packages/flutter/test/widgets/reassemble_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';

--- a/packages/flutter/test/widgets/render_object_element_test.dart
+++ b/packages/flutter/test/widgets/render_object_element_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/rendering.dart';
@@ -12,7 +10,7 @@ import 'package:flutter/widgets.dart';
 @immutable
 class Pair<T> {
  const Pair(this.first, this.second);
-  final T first;
+  final T? first;
  final T second;
  @override
@@ -31,10 +29,10 @@ class Pair<T> {
 /// and the other child in the bottom half. It will swap which child is on top
 /// and which is on bottom every time the widget is rendered.
 abstract class Swapper extends RenderObjectWidget {
-  const Swapper({this.stable, this.swapper});
+  const Swapper({ this.stable, this.swapper });
-  final Widget stable;
+  final Widget? stable;
-  final Widget swapper;
+  final Widget? swapper;
  @override
  SwapperElement createElement();
@@ -45,8 +43,8 @@ abstract class Swapper extends RenderObjectWidget {
 class SwapperWithProperOverrides extends Swapper {
  const SwapperWithProperOverrides({
-    Widget stable,
+    Widget? stable,
-    Widget swapper,
+    Widget? swapper,
  }) : super(stable: stable, swapper: swapper);
  @override
@@ -55,8 +53,8 @@ class SwapperWithProperOverrides extends Swapper {
 class SwapperWithNoOverrides extends Swapper {
  const SwapperWithNoOverrides({
-    Widget stable,
+    Widget? stable,
-    Widget swapper,
+    Widget? swapper,
  }) : super(stable: stable, swapper: swapper);
  @override
@@ -65,8 +63,8 @@ class SwapperWithNoOverrides extends Swapper {
 class SwapperWithDeprecatedOverrides extends Swapper {
  const SwapperWithDeprecatedOverrides({
-    Widget stable,
+    Widget? stable,
-    Widget swapper,
+    Widget? swapper,
  }) : super(stable: stable, swapper: swapper);
  @override
@@ -76,8 +74,8 @@ class SwapperWithDeprecatedOverrides extends Swapper {
 abstract class SwapperElement extends RenderObjectElement {
  SwapperElement(Swapper widget) : super(widget);
-  Element stable;
+  Element? stable;
-  Element swapper;
+  Element? swapper;
  bool swapperIsOnTop = true;
  List<dynamic> insertSlots = <dynamic>[];
  List<Pair<dynamic>> moveSlots = <Pair<dynamic>>[];
@@ -92,9 +90,9 @@ abstract class SwapperElement extends RenderObjectElement {
  @override
  void visitChildren(ElementVisitor visitor) {
    if (stable != null)
-      visitor(stable);
+      visitor(stable!);
    if (swapper != null)
-      visitor(swapper);
+      visitor(swapper!);
  }
  @override
@@ -104,7 +102,7 @@ abstract class SwapperElement extends RenderObjectElement {
  }
  @override
-  void mount(Element parent, dynamic newSlot) {
+  void mount(Element? parent, dynamic newSlot) {
    super.mount(parent, newSlot);
    _updateChildren(widget);
  }
@@ -183,22 +181,22 @@ class SwapperElementWithDeprecatedOverrides extends SwapperElement {
 }
 class RenderSwapper extends RenderBox {
-  RenderBox _stable;
+  RenderBox? _stable;
-  RenderBox get stable => _stable;
+  RenderBox? get stable => _stable;
-  set stable(RenderBox child) {
+  set stable(RenderBox? child) {
    if (child == _stable)
      return;
    if (_stable != null)
-      dropChild(_stable);
+      dropChild(_stable!);
    _stable = child;
    if (child != null)
      adoptChild(child);
  }
-  bool _swapperIsOnTop;
+  bool? _swapperIsOnTop;
-  RenderBox _swapper;
+  RenderBox? _swapper;
-  RenderBox get swapper => _swapper;
+  RenderBox? get swapper => _swapper;
-  void setSwapper(RenderBox child, bool isOnTop) {
+  void setSwapper(RenderBox? child, bool isOnTop) {
    if (isOnTop != _swapperIsOnTop) {
      _swapperIsOnTop = isOnTop;
      markNeedsLayout();
@@ -206,7 +204,7 @@ class RenderSwapper extends RenderBox {
    if (child == _swapper)
      return;
    if (_swapper != null)
-      dropChild(_swapper);
+      dropChild(_swapper!);
    _swapper = child;
    if (child != null)
      adoptChild(child);
@@ -215,9 +213,9 @@ class RenderSwapper extends RenderBox {
  @override
  void visitChildren(RenderObjectVisitor visitor) {
    if (_stable != null)
-      visitor(_stable);
+      visitor(_stable!);
    if (_swapper != null)
-      visitor(_swapper);
+      visitor(_swapper!);
  }
  @override
@@ -244,21 +242,21 @@ class RenderSwapper extends RenderBox {
      maxHeight: constraints.maxHeight / 2,
    );
    if (_stable != null) {
-      final BoxParentData stableParentData = _stable.parentData as BoxParentData;
+      final BoxParentData stableParentData = _stable!.parentData! as BoxParentData;
-      _stable.layout(childConstraints);
+      _stable!.layout(childConstraints);
-      stableParentData.offset = _swapperIsOnTop ? bottomOffset : topOffset;
+      stableParentData.offset = _swapperIsOnTop! ? bottomOffset : topOffset;
    }
    if (_swapper != null) {
-      final BoxParentData swapperParentData = _swapper.parentData as BoxParentData;
+      final BoxParentData swapperParentData = _swapper!.parentData! as BoxParentData;
-      _swapper.layout(childConstraints);
+      _swapper!.layout(childConstraints);
-      swapperParentData.offset = _swapperIsOnTop ? topOffset : bottomOffset;
+      swapperParentData.offset = _swapperIsOnTop! ? topOffset : bottomOffset;
    }
  }
  @override
  void paint(PaintingContext context, Offset offset) {
    visitChildren((RenderObject child) {
-      final BoxParentData childParentData = child.parentData as BoxParentData;
+      final BoxParentData childParentData = child.parentData! as BoxParentData;
      context.paintChild(child, offset + childParentData.offset);
    });
  }
@@ -269,7 +267,7 @@ class RenderSwapper extends RenderBox {
  }
 }
-BoxParentData parentDataFor(RenderObject renderObject) => renderObject.parentData as BoxParentData;
+BoxParentData parentDataFor(RenderObject renderObject) => renderObject.parentData! as BoxParentData;
 void main() {
  testWidgets('RenderObjectElement *RenderObjectChild methods get called with correct arguments', (WidgetTester tester) async {
@@ -356,7 +354,7 @@ void main() {
    expect(swapper.insertSlots.length, 2);
    expect(swapper.moveSlots.length, 1);
    expect(swapper.removeSlots.length, 2);
-    expect(swapper.removeSlots, <bool>[null,null]);
+    expect(swapper.removeSlots, <bool?>[null,null]);
  });
  testWidgets('RenderObjectElement *ChildRenderObject methods fail with deprecation message', (WidgetTester tester) async {

--- a/packages/flutter/test/widgets/render_object_widget_test.dart
+++ b/packages/flutter/test/widgets/render_object_widget_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';
@@ -16,8 +14,8 @@ final BoxDecoration kBoxDecorationC = BoxDecoration(border: nonconst(null));
 class TestWidget extends StatelessWidget {
  const TestWidget({
-    Key key,
+    Key? key,
-    this.child,
+    required this.child,
  }) : super(key: key);
  final Widget child;
@@ -27,18 +25,16 @@ class TestWidget extends StatelessWidget {
 }
 class TestOrientedBox extends SingleChildRenderObjectWidget {
-  const TestOrientedBox({ Key key, Widget child }) : super(key: key, child: child);
+  const TestOrientedBox({ Key? key, Widget? child }) : super(key: key, child: child);
  Decoration _getDecoration(BuildContext context) {
-    final Orientation orientation = MediaQuery.of(context).orientation;
+    final Orientation orientation = MediaQuery.of(context)!.orientation;
    switch (orientation) {
      case Orientation.landscape:
        return const BoxDecoration(color: Color(0xFF00FF00));
      case Orientation.portrait:
        return const BoxDecoration(color: Color(0xFF0000FF));
    }
-    assert(orientation != null);
-    return null;
  }
  @override
@@ -51,7 +47,7 @@ class TestOrientedBox extends SingleChildRenderObjectWidget {
 }
 class TestNonVisitingWidget extends SingleChildRenderObjectWidget {
-  const TestNonVisitingWidget({ Key key, Widget child }) : super(key: key, child: child);
+  const TestNonVisitingWidget({ Key? key, required Widget child }) : super(key: key, child: child);
  @override
  RenderObject createRenderObject(BuildContext context) => TestNonVisitingRenderObject();
@@ -60,13 +56,13 @@ class TestNonVisitingWidget extends SingleChildRenderObjectWidget {
 class TestNonVisitingRenderObject extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
  @override
  void performLayout() {
-    child.layout(constraints, parentUsesSize: true);
+    child!.layout(constraints, parentUsesSize: true);
-    size = child.size;
+    size = child!.size;
  }
  @override
  void paint(PaintingContext context, Offset offset) {
-    context.paintChild(child, offset);
+    context.paintChild(child!, offset);
  }
  @override
@@ -107,7 +103,7 @@ void main() {
      expect(renderObject.position, equals(DecorationPosition.background));
      expect(renderObject.child, isNotNull);
      expect(renderObject.child, isA<RenderDecoratedBox>());
-      final RenderDecoratedBox child = renderObject.child as RenderDecoratedBox;
+      final RenderDecoratedBox child = renderObject.child! as RenderDecoratedBox;
      expect(child.decoration, equals(kBoxDecorationB));
      expect(child.position, equals(DecorationPosition.background));
      expect(child.child, isNull);
@@ -196,10 +192,10 @@ void main() {
    expect(element.renderObject, isA<RenderDecoratedBox>());
    final RenderDecoratedBox parent = element.renderObject as RenderDecoratedBox;
    expect(parent.child, isA<RenderDecoratedBox>());
-    final RenderDecoratedBox child = parent.child as RenderDecoratedBox;
+    final RenderDecoratedBox child = parent.child! as RenderDecoratedBox;
    expect(child.decoration, equals(kBoxDecorationB));
    expect(child.child, isA<RenderDecoratedBox>());
-    final RenderDecoratedBox grandChild = child.child as RenderDecoratedBox;
+    final RenderDecoratedBox grandChild = child.child! as RenderDecoratedBox;
    expect(grandChild.decoration, equals(kBoxDecorationC));
    expect(grandChild.child, isNull);

--- a/packages/flutter/test/widgets/reparent_state_harder_test.dart
+++ b/packages/flutter/test/widgets/reparent_state_harder_test.dart
@@ -2,15 +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/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 // This is a regression test for https://github.com/flutter/flutter/issues/5588.
 class OrderSwitcher extends StatefulWidget {
-  const OrderSwitcher({ Key key, this.a, this.b }) : super(key: key);
+  const OrderSwitcher({
+    Key? key,
+    required this.a,
+    required this.b,
+  }) : super(key: key);
  final Widget a;
  final Widget b;
@@ -47,7 +49,7 @@ class OrderSwitcherState extends State<OrderSwitcher> {
 }
 class DummyStatefulWidget extends StatefulWidget {
-  const DummyStatefulWidget(Key key) : super(key: key);
+  const DummyStatefulWidget(Key? key) : super(key: key);
  @override
  DummyStatefulWidgetState createState() => DummyStatefulWidgetState();
@@ -60,18 +62,18 @@ class DummyStatefulWidgetState extends State<DummyStatefulWidget> {
 class RekeyableDummyStatefulWidgetWrapper extends StatefulWidget {
  const RekeyableDummyStatefulWidgetWrapper({
-    Key key,
+    Key? key,
    this.child,
-    this.initialKey,
+    required this.initialKey,
  }) : super(key: key);
-  final Widget child;
+  final Widget? child;
  final GlobalKey initialKey;
  @override
  RekeyableDummyStatefulWidgetWrapperState createState() => RekeyableDummyStatefulWidgetWrapperState();
 }
 class RekeyableDummyStatefulWidgetWrapperState extends State<RekeyableDummyStatefulWidgetWrapper> {
-  GlobalKey _key;
+  GlobalKey? _key;
  @override
  void initState() {
@@ -79,7 +81,7 @@ class RekeyableDummyStatefulWidgetWrapperState extends State<RekeyableDummyState
    _key = widget.initialKey;
  }
-  void _setChild(GlobalKey value) {
+  void _setChild(GlobalKey? value) {
    setState(() {
      _key = value;
    });
@@ -160,7 +162,7 @@ void main() {
    expect(find.byType(RekeyableDummyStatefulWidgetWrapper), findsNWidgets(2));
    expect(find.byType(DummyStatefulWidget), findsNWidgets(2));
-    keyRoot.currentState.switchChildren();
+    keyRoot.currentState!.switchChildren();
    final List<State> states = tester.stateList(find.byType(RekeyableDummyStatefulWidgetWrapper)).toList();
    final RekeyableDummyStatefulWidgetWrapperState a = states[0] as RekeyableDummyStatefulWidgetWrapperState;
    a._setChild(null);

--- a/packages/flutter/test/widgets/reparent_state_test.dart
+++ b/packages/flutter/test/widgets/reparent_state_test.dart
@@ -2,33 +2,31 @@
 // 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 StateMarker extends StatefulWidget {
-  const StateMarker({ Key key, this.child }) : super(key: key);
+  const StateMarker({ Key? key, this.child }) : super(key: key);
-  final Widget child;
+  final Widget? child;
  @override
  StateMarkerState createState() => StateMarkerState();
 }
 class StateMarkerState extends State<StateMarker> {
-  String marker;
+  String? marker;
  @override
  Widget build(BuildContext context) {
    if (widget.child != null)
-      return widget.child;
+      return widget.child!;
    return Container();
  }
 }
 class DeactivateLogger extends StatefulWidget {
-  const DeactivateLogger({ Key key, this.log }) : super(key: key);
+  const DeactivateLogger({ required Key key, required this.log }) : super(key: key);
  final List<String> log;
@@ -73,9 +71,9 @@ void main() {
      ),
    );
-    final StateMarkerState leftState = left.currentState as StateMarkerState;
+    final StateMarkerState leftState = left.currentState! as StateMarkerState;
    leftState.marker = 'left';
-    final StateMarkerState rightState = right.currentState as StateMarkerState;
+    final StateMarkerState rightState = right.currentState! as StateMarkerState;
    rightState.marker = 'right';
    final StateMarkerState grandchildState = tester.state(find.byWidget(grandchild));
@@ -144,9 +142,9 @@ void main() {
      ),
    );
-    final StateMarkerState leftState = left.currentState as StateMarkerState;
+    final StateMarkerState leftState = left.currentState! as StateMarkerState;
    leftState.marker = 'left';
-    final StateMarkerState rightState = right.currentState as StateMarkerState;
+    final StateMarkerState rightState = right.currentState! as StateMarkerState;
    rightState.marker = 'right';
    final StateMarkerState grandchildState = tester.state(find.byWidget(grandchild));
@@ -198,7 +196,7 @@ void main() {
    await tester.pumpWidget(StateMarker(key: key));
-    final StateMarkerState keyState = key.currentState as StateMarkerState;
+    final StateMarkerState keyState = key.currentState! as StateMarkerState;
    keyState.marker = 'marked';
    await tester.pumpWidget(
@@ -237,7 +235,7 @@ void main() {
      ],
    ));
-    final StateMarkerState keyState = key.currentState as StateMarkerState;
+    final StateMarkerState keyState = key.currentState!as StateMarkerState;
    keyState.marker = 'marked';
    await tester.pumpWidget(Stack(
@@ -275,7 +273,7 @@ void main() {
      ],
    ));
-    final StateMarkerState keyState = key.currentState as StateMarkerState;
+    final StateMarkerState keyState = key.currentState! as StateMarkerState;
    keyState.marker = 'marked';
    await tester.pumpWidget(Stack(

--- a/packages/flutter/test/widgets/reparent_state_with_layout_builder_test.dart
+++ b/packages/flutter/test/widgets/reparent_state_with_layout_builder_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 window;
 import 'package:flutter/material.dart';
@@ -12,7 +10,7 @@ import 'package:flutter_test/flutter_test.dart';
 // This is a regression test for https://github.com/flutter/flutter/issues/5840.
 class Bar extends StatefulWidget {
-  const Bar({ Key key }) : super(key: key);
+  const Bar({ Key? key }) : super(key: key);
  @override
  BarState createState() => BarState();
 }
@@ -49,7 +47,7 @@ class BarState extends State<Bar> {
 }
 class StatefulCreationCounter extends StatefulWidget {
-  const StatefulCreationCounter({ Key key }) : super(key: key);
+  const StatefulCreationCounter({ Key? key }) : super(key: key);
  @override
  StatefulCreationCounterState createState() => StatefulCreationCounterState();
@@ -82,9 +80,9 @@ void main() {
  testWidgets('Clean then reparent with dependencies', (WidgetTester tester) async {
    int layoutBuilderBuildCount = 0;
-    StateSetter keyedSetState;
+    late StateSetter keyedSetState;
-    StateSetter layoutBuilderSetState;
+    late StateSetter layoutBuilderSetState;
-    StateSetter childSetState;
+    late StateSetter childSetState;
    final GlobalKey key = GlobalKey();
    final Widget keyedWidget = StatefulBuilder(

--- a/packages/flutter/test/widgets/restorable_property_test.dart
+++ b/packages/flutter/test/widgets/restorable_property_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/services.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -19,14 +17,6 @@ void main() {
    expect(() => _TestRestorableValue().value, throwsAssertionError);
  });
-  testWidgets('cannot initialize with null', (WidgetTester tester) async {
-    expect(() => RestorableNum<num>(null), throwsAssertionError);
-    expect(() => RestorableDouble(null), throwsAssertionError);
-    expect(() => RestorableInt(null), throwsAssertionError);
-    expect(() => RestorableString(null).value, throwsAssertionError);
-    expect(() => RestorableBool(null).value, throwsAssertionError);
-  });
  testWidgets('work when not in restoration scope', (WidgetTester tester) async {
    await tester.pumpWidget(const _RestorableWidget());
@@ -119,22 +109,6 @@ void main() {
    expect(find.text('guten tag'), findsOneWidget);
  });
-  testWidgets('cannot set to null', (WidgetTester tester) async {
-    await tester.pumpWidget(const RootRestorationScope(
-      restorationId: 'root-child',
-      child: _RestorableWidget(),
-    ));
-    expect(find.text('hello world'), findsOneWidget);
-    final _RestorableWidgetState state = tester.state(find.byType(_RestorableWidget));
-    expect(() => state.numValue.value = null, throwsAssertionError);
-    expect(() => state.doubleValue.value = null, throwsAssertionError);
-    expect(() => state.intValue.value = null, throwsAssertionError);
-    expect(() => state.stringValue.value = null, throwsAssertionError);
-    expect(() => state.boolValue.value = null, throwsAssertionError);
-  });
  testWidgets('restore to older state', (WidgetTester tester) async {
    await tester.pumpWidget(const RootRestorationScope(
      restorationId: 'root-child',
@@ -320,7 +294,7 @@ class _TestRestorableValue extends RestorableValue<Object> {
  int didUpdateValueCallCount = 0;
  @override
-  void didUpdateValue(Object oldValue) {
+  void didUpdateValue(Object? oldValue) {
    didUpdateValueCallCount++;
    notifyListeners();
  }
@@ -337,7 +311,7 @@ class _TestRestorableValue extends RestorableValue<Object> {
 }
 class _RestorableWidget extends StatefulWidget {
-  const _RestorableWidget({Key key}) : super(key: key);
+  const _RestorableWidget({Key? key}) : super(key: key);
  @override
  State<_RestorableWidget> createState() => _RestorableWidgetState();
@@ -353,7 +327,7 @@ class _RestorableWidgetState extends State<_RestorableWidget> with RestorationMi
  final _TestRestorableValue objectValue = _TestRestorableValue();
  @override
-  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
    registerForRestoration(numValue, 'num');
    registerForRestoration(doubleValue, 'double');
    registerForRestoration(intValue, 'int');
@@ -369,7 +343,7 @@ class _RestorableWidgetState extends State<_RestorableWidget> with RestorationMi
  @override
  Widget build(BuildContext context) {
-    return Text(stringValue.value ?? 'null', textDirection: TextDirection.ltr,);
+    return Text(stringValue.value, textDirection: TextDirection.ltr,);
  }
  @override