Migrate non-test files in flutter/test (#67098)

packages/flutter/test/painting/decoration_test.dart

@@ -58,6 +58,10 @@ class SynchronousErrorTestImageProvider extends ImageProvider<int> {
 }
 
 class AsyncTestImageProvider extends ImageProvider<int> {
+  AsyncTestImageProvider(this.image);
+
+  final ui.Image image;
+
   @override
   Future<int> obtainKey(ImageConfiguration configuration) {
     return Future<int>.value(2);
@@ -66,7 +70,7 @@ class AsyncTestImageProvider extends ImageProvider<int> {
   @override
   ImageStreamCompleter load(int key, DecoderCallback decode) {
     return OneFrameImageStreamCompleter(
-      Future<ImageInfo>.value(TestImageInfo(key))
+      Future<ImageInfo>.value(TestImageInfo(key, image: image))
     );
   }
 }
@@ -147,9 +151,10 @@ void main() {
     expect(onChangedCalled, equals(false));
   });
 
-  test('BoxDecorationImageListenerAsync', () {
+  test('BoxDecorationImageListenerAsync', () async {
+    final ui.Image image = await createTestImage(width: 10, height: 10);
     FakeAsync().run((FakeAsync async)  {
-      final ImageProvider imageProvider = AsyncTestImageProvider();
+      final ImageProvider imageProvider = AsyncTestImageProvider(image);
       final DecorationImage backgroundImage = DecorationImage(image: imageProvider);
 
       final BoxDecoration boxDecoration = BoxDecoration(image: backgroundImage);

packages/flutter/test/painting/fake_codec.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 Codec, FrameInfo, instantiateImageCodec;
 
@@ -28,9 +26,9 @@ class FakeCodec implements ui.Codec {
   static Future<FakeCodec> fromData(Uint8List data) async {
     final ui.Codec codec = await ui.instantiateImageCodec(data);
     final int frameCount = codec.frameCount;
-    final List<ui.FrameInfo> frameInfos = List<ui.FrameInfo>(frameCount);
+    final List<ui.FrameInfo> frameInfos = <ui.FrameInfo>[];
     for (int i = 0; i < frameCount; i += 1)
-      frameInfos[i] = await codec.getNextFrame();
+      frameInfos.add(await codec.getNextFrame());
     return FakeCodec._(frameCount, codec.repetitionCount, frameInfos);
   }
 

packages/flutter/test/painting/fake_image_provider.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 Codec;
 
 import 'package:flutter/foundation.dart';

packages/flutter/test/painting/image_test_utils.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:ui' as ui;
 
@@ -19,7 +17,7 @@ class TestImageProvider extends ImageProvider<TestImageProvider> {
   final ui.Image testImage;
 
   final Completer<ImageInfo> _completer = Completer<ImageInfo>.sync();
-  ImageConfiguration configuration;
+  ImageConfiguration? configuration;
   int loadCallCount = 0;
 
   @override

packages/flutter/test/painting/mocks_for_image_cache.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:ui' as ui show Image;
 
@@ -11,7 +9,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 
 class TestImageInfo implements ImageInfo {
-  const TestImageInfo(this.value, { this.image, this.scale = 1.0, this.debugLabel });
+  const TestImageInfo(this.value, { required this.image, this.scale = 1.0, this.debugLabel });
 
   @override
   final ui.Image image;
@@ -20,7 +18,7 @@ class TestImageInfo implements ImageInfo {
   final double scale;
 
   @override
-  final String debugLabel;
+  final String? debugLabel;
 
   final int value;
 
@@ -29,7 +27,7 @@ class TestImageInfo implements ImageInfo {
 }
 
 class TestImageProvider extends ImageProvider<int> {
-  const TestImageProvider(this.key, this.imageValue, { @required this.image })
+  const TestImageProvider(this.key, this.imageValue, { required this.image })
       : assert(image != null);
 
   final int key;
@@ -53,7 +51,7 @@ class TestImageProvider extends ImageProvider<int> {
 }
 
 class FailingTestImageProvider extends TestImageProvider {
-  const FailingTestImageProvider(int key, int imageValue, { ui.Image image }) : super(key, imageValue, image: image);
+  const FailingTestImageProvider(int key, int imageValue, { required ui.Image image }) : super(key, imageValue, image: image);
 
   @override
   ImageStreamCompleter load(int key, DecoderCallback decode) {
@@ -63,7 +61,7 @@ class FailingTestImageProvider extends TestImageProvider {
 
 Future<ImageInfo> extractOneFrame(ImageStream stream) {
   final Completer<ImageInfo> completer = Completer<ImageInfo>();
-  ImageStreamListener listener;
+  late ImageStreamListener listener;
   listener = ImageStreamListener((ImageInfo image, bool synchronousCall) {
     completer.complete(image);
     stream.removeListener(listener);

packages/flutter/test/painting/painting_utils.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;
 
@@ -17,7 +15,7 @@ class PaintingBindingSpy extends BindingBase with SchedulerBinding, ServicesBind
   int get instantiateImageCodecCalledCount => counter;
 
   @override
-  Future<ui.Codec> instantiateImageCodec(Uint8List list, {int cacheWidth, int cacheHeight, bool allowUpscaling = false}) {
+  Future<ui.Codec> instantiateImageCodec(Uint8List list, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
     counter++;
     return ui.instantiateImageCodec(list);
   }

packages/flutter/test/rendering/mouse_tracking_test_utils.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;
 
 import 'package:flutter/cupertino.dart';
@@ -20,7 +18,7 @@ class _TestHitTester extends RenderBox {
   final BoxHitTest hitTestOverride;
 
   @override
-  bool hitTest(BoxHitTestResult result, {ui.Offset position}) {
+  bool hitTest(BoxHitTestResult result, {required ui.Offset position}) {
     return hitTestOverride(result, position);
   }
 }
@@ -39,7 +37,7 @@ class TestMouseTrackerFlutterBinding extends BindingBase
     renderView.child = _TestHitTester(hitTest);
   }
 
-  SchedulerPhase _overridePhase;
+  SchedulerPhase? _overridePhase;
   @override
   SchedulerPhase get schedulerPhase => _overridePhase ?? super.schedulerPhase;
 
@@ -48,7 +46,7 @@ class TestMouseTrackerFlutterBinding extends BindingBase
   // In real apps this is done by the renderer binding, but in tests we have to
   // bypass the phase assertion of [MouseTracker.schedulePostFrameCheck].
   void scheduleMouseTrackerPostFrameCheck() {
-    final SchedulerPhase lastPhase = _overridePhase;
+    final SchedulerPhase? lastPhase = _overridePhase;
     _overridePhase = SchedulerPhase.persistentCallbacks;
     addPostFrameCallback((_) {
       mouseTracker.updateAllDevices(renderView.hitTestMouseTrackers);
@@ -77,13 +75,13 @@ class TestAnnotationTarget with Diagnosticable implements MouseTrackerAnnotation
   const TestAnnotationTarget({this.onEnter, this.onHover, this.onExit, this.cursor = MouseCursor.defer});
 
   @override
-  final PointerEnterEventListener onEnter;
+  final PointerEnterEventListener? onEnter;
 
   @override
-  final PointerHoverEventListener onHover;
+  final PointerHoverEventListener? onHover;
 
   @override
-  final PointerExitEventListener onExit;
+  final PointerExitEventListener? onExit;
 
   @override
   final MouseCursor cursor;
@@ -92,14 +90,14 @@ class TestAnnotationTarget with Diagnosticable implements MouseTrackerAnnotation
   void handleEvent(PointerEvent event, HitTestEntry entry) {
     if (event is PointerHoverEvent)
       if (onHover != null)
-        onHover(event);
+        onHover!(event);
   }
 }
 
 // A hit test entry that can be assigned with a [TestAnnotationTarget] and an
 // optional transform matrix.
 class TestAnnotationEntry extends HitTestEntry {
-  TestAnnotationEntry(TestAnnotationTarget target, [Matrix4 transform])
+  TestAnnotationEntry(TestAnnotationTarget target, [Matrix4? transform])
     : transform = transform ?? Matrix4.identity(), super(target);
 
   @override

packages/flutter/test/rendering/recording_canvas.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/src/rendering/layer.dart';
@@ -13,7 +11,7 @@ import 'package:flutter/src/rendering/layer.dart';
 /// Used by [TestRecordingCanvas] to trace canvas calls.
 class RecordedInvocation {
   /// Create a record for an invocation list.
-  const RecordedInvocation(this.invocation, { this.stack });
+  const RecordedInvocation(this.invocation, { required this.stack });
 
   /// The method that was called and its arguments.
   ///
@@ -74,7 +72,7 @@ class TestRecordingCanvas implements Canvas {
   }
 
   @override
-  void saveLayer(Rect bounds, Paint paint) {
+  void saveLayer(Rect? bounds, Paint paint) {
     _saveCount += 1;
     invocations.add(RecordedInvocation(_MethodCall(#saveLayer, <dynamic>[bounds, paint]), stack: StackTrace.current));
   }
@@ -106,27 +104,27 @@ class TestRecordingPaintingContext extends ClipContext implements PaintingContex
   }
 
   @override
-  ClipRectLayer pushClipRect(
+  ClipRectLayer? pushClipRect(
     bool needsCompositing,
     Offset offset,
     Rect clipRect,
     PaintingContextCallback painter, {
     Clip clipBehavior = Clip.hardEdge,
-    ClipRectLayer oldLayer,
+    ClipRectLayer? oldLayer,
   }) {
     clipRectAndPaint(clipRect.shift(offset), clipBehavior, clipRect.shift(offset), () => painter(this, offset));
     return null;
   }
 
   @override
-  ClipRRectLayer pushClipRRect(
+  ClipRRectLayer? pushClipRRect(
     bool needsCompositing,
     Offset offset,
     Rect bounds,
     RRect clipRRect,
     PaintingContextCallback painter, {
     Clip clipBehavior = Clip.antiAlias,
-    ClipRRectLayer oldLayer,
+    ClipRRectLayer? oldLayer,
   }) {
     assert(clipBehavior != null);
     clipRRectAndPaint(clipRRect.shift(offset), clipBehavior, bounds.shift(offset), () => painter(this, offset));
@@ -134,26 +132,26 @@ class TestRecordingPaintingContext extends ClipContext implements PaintingContex
   }
 
   @override
-  ClipPathLayer pushClipPath(
+  ClipPathLayer? pushClipPath(
     bool needsCompositing,
     Offset offset,
     Rect bounds,
     Path clipPath,
     PaintingContextCallback painter, {
     Clip clipBehavior = Clip.antiAlias,
-    ClipPathLayer oldLayer,
+    ClipPathLayer? oldLayer,
   }) {
     clipPathAndPaint(clipPath.shift(offset), clipBehavior, bounds.shift(offset), () => painter(this, offset));
     return null;
   }
 
   @override
-  TransformLayer pushTransform(
+  TransformLayer? pushTransform(
     bool needsCompositing,
     Offset offset,
     Matrix4 transform,
     PaintingContextCallback painter, {
-    TransformLayer oldLayer,
+    TransformLayer? oldLayer,
   }) {
     canvas.save();
     canvas.transform(transform.storage);
@@ -163,17 +161,25 @@ class TestRecordingPaintingContext extends ClipContext implements PaintingContex
   }
 
   @override
-  OpacityLayer pushOpacity(Offset offset, int alpha, PaintingContextCallback painter,
-      { OpacityLayer oldLayer }) {
-    canvas.saveLayer(null, null); // TODO(ianh): Expose the alpha somewhere.
+  OpacityLayer pushOpacity(
+    Offset offset,
+    int alpha,
+    PaintingContextCallback painter, {
+    OpacityLayer? oldLayer,
+  }) {
+    canvas.saveLayer(null, Paint()); // TODO(ianh): Expose the alpha somewhere.
     painter(this, offset);
     canvas.restore();
-    return null;
+    return OpacityLayer();
   }
 
   @override
-  void pushLayer(Layer childLayer, PaintingContextCallback painter, Offset offset,
-      { Rect childPaintBounds }) {
+  void pushLayer(
+    Layer childLayer,
+    PaintingContextCallback painter,
+    Offset offset, {
+    Rect? childPaintBounds,
+  }) {
     painter(this, offset);
   }
 
@@ -204,7 +210,7 @@ class _MethodCall implements Invocation {
   List<Type> get typeArguments => _typeArguments;
 }
 
-String _valueName(Object value) {
+String _valueName(Object? value) {
   if (value is double)
     return value.toStringAsFixed(1);
   return value.toString();
@@ -228,7 +234,7 @@ String _describeInvocation(Invocation call) {
     buffer.write('(');
     buffer.writeAll(call.positionalArguments.map<String>(_valueName), ', ');
     String separator = call.positionalArguments.isEmpty ? '' : ', ';
-    call.namedArguments.forEach((Symbol name, Object value) {
+    call.namedArguments.forEach((Symbol name, Object? value) {
       buffer.write(separator);
       buffer.write(_symbolName(name));
       buffer.write(': ');

packages/flutter/test/rendering/rendering_tester.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/foundation.dart';
@@ -29,7 +27,7 @@ class TestRenderingFlutterBinding extends BindingBase with SchedulerBinding, Ser
   TestRenderingFlutterBinding({ this.onErrors }) {
     FlutterError.onError = (FlutterErrorDetails details) {
       FlutterError.dumpErrorToConsole(details);
-      Zone.current.parent.handleUncaughtError(details.exception, details.stack);
+      Zone.current.parent!.handleUncaughtError(details.exception as Object, details.stack!);
     };
   }
 
@@ -40,14 +38,14 @@ class TestRenderingFlutterBinding extends BindingBase with SchedulerBinding, Ser
   /// This function is expected to inspect these errors and decide whether they
   /// are expected or not. Use [takeFlutterErrorDetails] to take one error at a
   /// time, or [takeAllFlutterErrorDetails] to iterate over all errors.
-  VoidCallback onErrors;
+  VoidCallback? onErrors;
 
   /// Returns the error least recently caught by [FlutterError] and removes it
   /// from the list of captured errors.
   ///
   /// Returns null if no errors were captures, or if the list was exhausted by
   /// calling this method repeatedly.
-  FlutterErrorDetails takeFlutterErrorDetails() {
+  FlutterErrorDetails? takeFlutterErrorDetails() {
     if (_errors.isEmpty) {
       return null;
     }
@@ -87,7 +85,7 @@ class TestRenderingFlutterBinding extends BindingBase with SchedulerBinding, Ser
   @override
   void drawFrame() {
     assert(phase != EnginePhase.build, 'rendering_tester does not support testing the build phase; use flutter_test instead');
-    final FlutterExceptionHandler oldErrorHandler = FlutterError.onError;
+    final FlutterExceptionHandler? oldErrorHandler = FlutterError.onError;
     FlutterError.onError = (FlutterErrorDetails details) {
       _errors.add(details);
     };
@@ -113,7 +111,7 @@ class TestRenderingFlutterBinding extends BindingBase with SchedulerBinding, Ser
       FlutterError.onError = oldErrorHandler;
       if (_errors.isNotEmpty) {
         if (onErrors != null) {
-          onErrors();
+          onErrors!();
           if (_errors.isNotEmpty) {
             _errors.forEach(FlutterError.dumpErrorToConsole);
             fail('There are more errors than the test inspected using TestRenderingFlutterBinding.takeFlutterErrorDetails.');
@@ -127,11 +125,9 @@ class TestRenderingFlutterBinding extends BindingBase with SchedulerBinding, Ser
   }
 }
 
-TestRenderingFlutterBinding _renderer;
-TestRenderingFlutterBinding get renderer {
-  _renderer ??= TestRenderingFlutterBinding();
-  return _renderer;
-}
+late final TestRenderingFlutterBinding _renderer = TestRenderingFlutterBinding();
+TestRenderingFlutterBinding get renderer => _renderer;
+
 
 /// Place the box in the render tree, at the given size and with the given
 /// alignment on the screen.
@@ -149,10 +145,10 @@ TestRenderingFlutterBinding get renderer {
 /// If `onErrors` is not null, it is set as [TestRenderingFlutterBinding.onError].
 void layout(
   RenderBox box, {
-  BoxConstraints constraints,
+  BoxConstraints? constraints,
   Alignment alignment = Alignment.center,
   EnginePhase phase = EnginePhase.layout,
-  VoidCallback onErrors,
+  VoidCallback? onErrors,
 }) {
   assert(box != null); // If you want to just repump the last box, call pumpFrame().
   assert(box.parent == null); // We stick the box in another, so you can't reuse it easily, sorry.
@@ -175,7 +171,7 @@ void layout(
 /// Pumps a single frame.
 ///
 /// If `onErrors` is not null, it is set as [TestRenderingFlutterBinding.onError].
-void pumpFrame({ EnginePhase phase = EnginePhase.layout, VoidCallback onErrors }) {
+void pumpFrame({ EnginePhase phase = EnginePhase.layout, VoidCallback? onErrors }) {
   assert(renderer != null);
   assert(renderer.renderView != null);
   assert(renderer.renderView.child != null); // call layout() first!
@@ -189,7 +185,7 @@ void pumpFrame({ EnginePhase phase = EnginePhase.layout, VoidCallback onErrors }
 }
 
 class TestCallbackPainter extends CustomPainter {
-  const TestCallbackPainter({ this.onPaint });
+  const TestCallbackPainter({ required this.onPaint });
 
   final VoidCallback onPaint;
 
@@ -251,25 +247,25 @@ class FakeTickerProvider implements TickerProvider {
 
 class FakeTicker implements Ticker {
   @override
-  bool muted;
+  bool muted = false;
 
   @override
   void absorbTicker(Ticker originalTicker) { }
 
   @override
-  String get debugLabel => null;
+  String? get debugLabel => null;
 
   @override
-  bool get isActive => null;
+  bool get isActive => throw UnimplementedError();
 
   @override
-  bool get isTicking => null;
+  bool get isTicking => throw UnimplementedError();
 
   @override
-  bool get scheduled => null;
+  bool get scheduled => throw UnimplementedError();
 
   @override
-  bool get shouldScheduleTick => null;
+  bool get shouldScheduleTick => throw UnimplementedError();
 
   @override
   void dispose() { }
@@ -279,7 +275,7 @@ class FakeTicker implements Ticker {
 
   @override
   TickerFuture start() {
-    return null;
+    throw UnimplementedError();
   }
 
   @override
@@ -301,7 +297,14 @@ class TestClipPaintingContext extends PaintingContext {
   TestClipPaintingContext() : super(ContainerLayer(), Rect.zero);
 
   @override
-  ClipRectLayer pushClipRect(bool needsCompositing, Offset offset, Rect clipRect, PaintingContextCallback painter, {Clip clipBehavior = Clip.hardEdge, ClipRectLayer oldLayer}) {
+  ClipRectLayer? pushClipRect(
+    bool needsCompositing,
+    Offset offset,
+    Rect clipRect,
+    PaintingContextCallback painter, {
+    Clip clipBehavior = Clip.hardEdge,
+    ClipRectLayer? oldLayer,
+  }) {
     this.clipBehavior = clipBehavior;
     return null;
   }
@@ -310,7 +313,7 @@ class TestClipPaintingContext extends PaintingContext {
 }
 
 void expectOverflowedErrors() {
-  final FlutterErrorDetails errorDetails = renderer.takeFlutterErrorDetails();
+  final FlutterErrorDetails errorDetails = renderer.takeFlutterErrorDetails()!;
   final bool overflowed = errorDetails.toString().contains('overflowed');
   if (!overflowed) {
     FlutterError.reportError(errorDetails);

packages/flutter/test/services/restoration.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 'package:flutter/services.dart';
@@ -53,15 +51,15 @@ class MockRestorationManager extends TestRestorationManager {
   int rootBucketAccessed = 0;
 
   @override
-  Future<RestorationBucket> get rootBucket {
+  Future<RestorationBucket?> get rootBucket {
     rootBucketAccessed++;
     return _rootBucket;
   }
-  Future<RestorationBucket> _rootBucket;
-  set rootBucket(Future<RestorationBucket> value) {
+  late Future<RestorationBucket?> _rootBucket;
+  set rootBucket(Future<RestorationBucket?> value) {
     _rootBucket = value;
     _isRestoring = true;
-    ServicesBinding.instance.addPostFrameCallback((Duration _) {
+    ServicesBinding.instance!.addPostFrameCallback((Duration _) {
       _isRestoring = false;
     });
     notifyListeners();
@@ -69,7 +67,7 @@ class MockRestorationManager extends TestRestorationManager {
 
   @override
   bool get isReplacing => _isRestoring;
-  bool _isRestoring;
+  bool _isRestoring = false;
 
   @override
   Future<void> sendToEngine(Uint8List encodedData) {

packages/flutter/test/widgets/editable_text_utils.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';
@@ -13,7 +11,7 @@ RenderEditable findRenderEditable(WidgetTester tester) {
   final RenderObject root = tester.renderObject(find.byType(EditableText));
   expect(root, isNotNull);
 
-  RenderEditable renderEditable;
+  late RenderEditable renderEditable;
   void recursiveFinder(RenderObject child) {
     if (child is RenderEditable) {
       renderEditable = child;

packages/flutter/test/widgets/gesture_utils.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_test/flutter_test.dart';
 

packages/flutter/test/widgets/observer_tester.dart

@@ -2,49 +2,47 @@
 // 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';
 
-typedef OnObservation = void Function(Route<dynamic> route, Route<dynamic> previousRoute);
+typedef OnObservation = void Function(Route<dynamic>? route, Route<dynamic>? previousRoute);
 
 /// A trivial observer for testing the navigator.
 class TestObserver extends NavigatorObserver {
-  OnObservation onPushed;
-  OnObservation onPopped;
-  OnObservation onRemoved;
-  OnObservation onReplaced;
-  OnObservation onStartUserGesture;
+  OnObservation? onPushed;
+  OnObservation? onPopped;
+  OnObservation? onRemoved;
+  OnObservation? onReplaced;
+  OnObservation? onStartUserGesture;
 
   @override
-  void didPush(Route<dynamic> route, Route<dynamic> previousRoute) {
+  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
     if (onPushed != null) {
-      onPushed(route, previousRoute);
+      onPushed!(route, previousRoute);
     }
   }
 
   @override
-  void didPop(Route<dynamic> route, Route<dynamic> previousRoute) {
+  void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) {
     if (onPopped != null) {
-      onPopped(route, previousRoute);
+      onPopped!(route, previousRoute);
     }
   }
 
   @override
-  void didRemove(Route<dynamic> route, Route<dynamic> previousRoute) {
+  void didRemove(Route<dynamic> route, Route<dynamic>? previousRoute) {
     if (onRemoved != null)
-      onRemoved(route, previousRoute);
+      onRemoved!(route, previousRoute);
   }
 
   @override
-  void didReplace({ Route<dynamic> oldRoute, Route<dynamic> newRoute }) {
+  void didReplace({ Route<dynamic>? oldRoute, Route<dynamic>? newRoute }) {
     if (onReplaced != null)
-      onReplaced(newRoute, oldRoute);
+      onReplaced!(newRoute, oldRoute);
   }
 
   @override
-  void didStartUserGesture(Route<dynamic> route, Route<dynamic> previousRoute) {
+  void didStartUserGesture(Route<dynamic> route, Route<dynamic>? previousRoute) {
     if (onStartUserGesture != null)
-      onStartUserGesture(route, previousRoute);
+      onStartUserGesture!(route, previousRoute);
   }
 }

packages/flutter/test/widgets/restoration.dart

@@ -2,24 +2,22 @@
 // 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';
 
 export '../services/restoration.dart';
 
 class BucketSpy extends StatefulWidget {
-  const BucketSpy({Key key, this.child}) : super(key: key);
+  const BucketSpy({Key? key, this.child}) : super(key: key);
 
-  final Widget child;
+  final Widget? child;
 
   @override
   State<BucketSpy> createState() => BucketSpyState();
 }
 
 class BucketSpyState extends State<BucketSpy> {
-  RestorationBucket bucket;
+  RestorationBucket? bucket;
 
   @override
   void didChangeDependencies() {

packages/flutter/test/widgets/states.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
-
 const List<String> kStates = <String>[
   'Alabama',
   'Alaska',

packages/flutter/test/widgets/test_border.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';
 
 typedef Logger = void Function(String caller);
@@ -20,19 +18,19 @@ class TestBorder extends ShapeBorder {
   ShapeBorder scale(double t) => TestBorder(onLog);
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     onLog('getInnerPath $rect $textDirection');
     return Path();
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     onLog('getOuterPath $rect $textDirection');
     return Path();
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     onLog('paint $rect $textDirection');
   }
 }

packages/flutter/test/widgets/test_widgets.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';
@@ -21,7 +19,7 @@ const BoxDecoration kBoxDecorationC = BoxDecoration(
 );
 
 class TestBuildCounter extends StatelessWidget {
-  const TestBuildCounter({ Key key }) : super(key: key);
+  const TestBuildCounter({ Key? key }) : super(key: key);
 
   static int buildCount = 0;
 
@@ -34,7 +32,7 @@ class TestBuildCounter extends StatelessWidget {
 
 
 class FlipWidget extends StatefulWidget {
-  const FlipWidget({ Key key, this.left, this.right }) : super(key: key);
+  const FlipWidget({ Key? key, required this.left, required this.right }) : super(key: key);
 
   final Widget left;
   final Widget right;

packages/flutter/test/widgets/text.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';
@@ -14,7 +12,7 @@ RenderEditable findRenderEditable(WidgetTester tester) {
   final RenderObject root = tester.renderObject(find.byType(EditableText));
   expect(root, isNotNull);
 
-  RenderEditable renderEditable;
+  late RenderEditable renderEditable;
   void recursiveFinder(RenderObject child) {
     if (child is RenderEditable) {
       renderEditable = child;

packages/flutter/test/widgets/widget_inspector_test_utils.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:convert';
 
@@ -12,48 +10,46 @@ import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-typedef InspectorServiceExtensionCallback = FutureOr<Map<String, Object>> Function(Map<String, String> parameters);
-
 class TestWidgetInspectorService extends Object with WidgetInspectorService {
-  final Map<String, InspectorServiceExtensionCallback> extensions = <String, InspectorServiceExtensionCallback>{};
+  final Map<String, ServiceExtensionCallback> extensions = <String, ServiceExtensionCallback>{};
 
-  final Map<String, List<Map<Object, Object>>> eventsDispatched = <String, List<Map<Object, Object>>>{};
+  final Map<String, List<Map<Object, Object?>>> eventsDispatched = <String, List<Map<Object, Object?>>>{};
 
   @override
   void registerServiceExtension({
-    @required String name,
-    @required FutureOr<Map<String, Object>> callback(Map<String, String> parameters),
+    required String name,
+    required ServiceExtensionCallback callback,
   }) {
     assert(!extensions.containsKey(name));
     extensions[name] = callback;
   }
 
   @override
-  void postEvent(String eventKind, Map<Object, Object> eventData) {
+  void postEvent(String eventKind, Map<Object, Object?> eventData) {
     getEventsDispatched(eventKind).add(eventData);
   }
 
-  List<Map<Object, Object>> getEventsDispatched(String eventKind) {
+  List<Map<Object, Object?>> getEventsDispatched(String eventKind) {
     return eventsDispatched.putIfAbsent(eventKind, () => <Map<Object, Object>>[]);
   }
 
-  Iterable<Map<Object, Object>> getServiceExtensionStateChangedEvents(String extensionName) {
+  Iterable<Map<Object, Object?>> getServiceExtensionStateChangedEvents(String extensionName) {
     return getEventsDispatched('Flutter.ServiceExtensionStateChanged')
-      .where((Map<Object, Object> event) => event['extension'] == extensionName);
+      .where((Map<Object, Object?> event) => event['extension'] == extensionName);
   }
 
-  Future<Object> testExtension(String name, Map<String, String> arguments) async {
+  Future<Object?> testExtension(String name, Map<String, String> arguments) async {
     expect(extensions, contains(name));
     // Encode and decode to JSON to match behavior using a real service
     // extension where only JSON is allowed.
-    return json.decode(json.encode(await extensions[name](arguments)))['result'];
+    return json.decode(json.encode(await extensions[name]!(arguments)))['result'];
   }
 
   Future<String> testBoolExtension(String name, Map<String, String> arguments) async {
     expect(extensions, contains(name));
     // Encode and decode to JSON to match behavior using a real service
     // extension where only JSON is allowed.
-    return json.decode(json.encode(await extensions[name](arguments)))['enabled'] as String;
+    return json.decode(json.encode(await extensions[name]!(arguments)))['enabled'] as String;
   }
 
   int rebuildCount = 0;
@@ -61,10 +57,10 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
   @override
   Future<void> forceRebuild() async {
     rebuildCount++;
-    final WidgetsBinding binding = WidgetsBinding.instance;
+    final WidgetsBinding binding = WidgetsBinding.instance!;
 
     if (binding.renderViewElement != null) {
-      binding.buildOwner.reassemble(binding.renderViewElement);
+      binding.buildOwner!.reassemble(binding.renderViewElement!);
     }
   }
 }