diff --git a/packages/flutter/test/painting/decoration_test.dart b/packages/flutter/test/painting/decoration_test.dart
index e85fa68ac6d..2d580e923c6 100644
--- a/packages/flutter/test/painting/decoration_test.dart
+++ b/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', () {
-    FakeAsync().run((FakeAsync async) {
-      final ImageProvider imageProvider = AsyncTestImageProvider();
+  test('BoxDecorationImageListenerAsync', () async {
+    final ui.Image image = await createTestImage(width: 10, height: 10);
+    FakeAsync().run((FakeAsync async)  {
+      final ImageProvider imageProvider = AsyncTestImageProvider(image);
       final DecorationImage backgroundImage = DecorationImage(image: imageProvider);
 
       final BoxDecoration boxDecoration = BoxDecoration(image: backgroundImage);
diff --git a/packages/flutter/test/painting/fake_codec.dart b/packages/flutter/test/painting/fake_codec.dart
index bce09c26b6e..7b9553146fc 100644
--- a/packages/flutter/test/painting/fake_codec.dart
+++ b/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);
   }
 
diff --git a/packages/flutter/test/painting/fake_image_provider.dart b/packages/flutter/test/painting/fake_image_provider.dart
index 92dadf965aa..c352adaaab2 100644
--- a/packages/flutter/test/painting/fake_image_provider.dart
+++ b/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';
diff --git a/packages/flutter/test/painting/image_test_utils.dart b/packages/flutter/test/painting/image_test_utils.dart
index 082e8ebbb81..4df2a48c44e 100644
--- a/packages/flutter/test/painting/image_test_utils.dart
+++ b/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
diff --git a/packages/flutter/test/painting/mocks_for_image_cache.dart b/packages/flutter/test/painting/mocks_for_image_cache.dart
index 899254cf588..e868db32b75 100644
--- a/packages/flutter/test/painting/mocks_for_image_cache.dart
+++ b/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);
diff --git a/packages/flutter/test/painting/painting_utils.dart b/packages/flutter/test/painting/painting_utils.dart
index fcd1f4748ce..3f23b48fcf0 100644
--- a/packages/flutter/test/painting/painting_utils.dart
+++ b/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);
   }
diff --git a/packages/flutter/test/rendering/mock_canvas.dart b/packages/flutter/test/rendering/mock_canvas.dart
index 9aa9c590b68..45447760727 100644
--- a/packages/flutter/test/rendering/mock_canvas.dart
+++ b/packages/flutter/test/rendering/mock_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 'dart:ui' as ui show Paragraph, Image;
 
 import 'package:flutter/foundation.dart';
@@ -102,14 +100,14 @@ abstract class PaintPattern {
   /// Calls are skipped until a call to [Canvas.translate] is found. The call's
   /// arguments are compared to those provided here. If any fail to match, or if
   /// no call to [Canvas.translate] is found, then the matcher fails.
-  void translate({ double x, double y });
+  void translate({ double? x, double? y });
 
   /// Indicates that a scale transform is expected next.
   ///
   /// Calls are skipped until a call to [Canvas.scale] is found. The call's
   /// arguments are compared to those provided here. If any fail to match, or if
   /// no call to [Canvas.scale] is found, then the matcher fails.
-  void scale({ double x, double y });
+  void scale({ double? x, double? y });
 
   /// Indicates that a rotate transform is expected next.
   ///
@@ -117,7 +115,7 @@ abstract class PaintPattern {
   /// argument is provided here, the call's argument is compared to it. If that
   /// fails to match, or if no call to [Canvas.rotate] is found, then the
   /// matcher fails.
-  void rotate({ double angle });
+  void rotate({ double? angle });
 
   /// Indicates that a save is expected next.
   ///
@@ -165,7 +163,7 @@ abstract class PaintPattern {
   ///
   /// Any calls made between the last matched call (if any) and the
   /// [Canvas.clipRect] call are ignored.
-  void clipRect({ Rect rect });
+  void clipRect({ Rect? rect });
 
   /// Indicates that a path clip is expected next.
   ///
@@ -177,7 +175,7 @@ abstract class PaintPattern {
   ///
   /// Any calls made between the last matched call (if any) and the
   /// [Canvas.clipPath] call are ignored.
-  void clipPath({ Matcher pathMatcher });
+  void clipPath({ Matcher? pathMatcher });
 
   /// Indicates that a rectangle is expected next.
   ///
@@ -195,7 +193,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void rect({ Rect rect, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void rect({ Rect? rect, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Indicates that a rounded rectangle clip is expected next.
   ///
@@ -207,7 +205,7 @@ abstract class PaintPattern {
   ///
   /// Any calls made between the last matched call (if any) and the
   /// [Canvas.clipRRect] call are ignored.
-  void clipRRect({ RRect rrect });
+  void clipRRect({ RRect? rrect });
 
   /// Indicates that a rounded rectangle is expected next.
   ///
@@ -225,7 +223,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void rrect({ RRect rrect, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void rrect({ RRect? rrect, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Indicates that a rounded rectangle outline is expected next.
   ///
@@ -243,7 +241,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void drrect({ RRect outer, RRect inner, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void drrect({ RRect? outer, RRect? inner, Color? color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
 
   /// Indicates that a circle is expected next.
   ///
@@ -261,7 +259,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void circle({ double x, double y, double radius, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void circle({ double? x, double? y, double? radius, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Indicates that a path is expected next.
   ///
@@ -284,7 +282,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void path({ Iterable<Offset> includes, Iterable<Offset> excludes, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void path({ Iterable<Offset>? includes, Iterable<Offset>? excludes, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Indicates that a line is expected next.
   ///
@@ -302,7 +300,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void line({ Offset p1, Offset p2, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void line({ Offset? p1, Offset? p2, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Indicates that an arc is expected next.
   ///
@@ -320,7 +318,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void arc({ Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void arc({ Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Indicates that a paragraph is expected next.
   ///
@@ -336,7 +334,7 @@ abstract class PaintPattern {
   /// offset.
   ///
   /// If no call to [Canvas.drawParagraph] was made, then this results in failure.
-  void paragraph({ ui.Paragraph paragraph, dynamic offset });
+  void paragraph({ ui.Paragraph? paragraph, dynamic offset });
 
   /// Indicates that a shadow is expected next.
   ///
@@ -357,7 +355,7 @@ abstract class PaintPattern {
   ///
   /// Any calls made between the last matched call (if any) and the
   /// [Canvas.drawShadow] call are ignored.
-  void shadow({ Iterable<Offset> includes, Iterable<Offset> excludes, Color color, double elevation, bool transparentOccluder });
+  void shadow({ Iterable<Offset>? includes, Iterable<Offset>? excludes, Color? color, double? elevation, bool? transparentOccluder });
 
   /// Indicates that an image is expected next.
   ///
@@ -375,7 +373,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void image({ ui.Image image, double x, double y, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void image({ ui.Image? image, double? x, double? y, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Indicates that an image subsection is expected next.
   ///
@@ -393,7 +391,7 @@ abstract class PaintPattern {
   /// painting has completed, not at the time of the call. If the same [Paint]
   /// object is reused multiple times, then this may not match the actual
   /// arguments as they were seen by the method.
-  void drawImageRect({ ui.Image image, Rect source, Rect destination, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+  void drawImageRect({ ui.Image? image, Rect? source, Rect? destination, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style });
 
   /// Provides a custom matcher.
   ///
@@ -451,12 +449,12 @@ class _PathMatcher extends Matcher {
   List<Offset> excludes;
 
   @override
-  bool matches(Object object, Map<dynamic, dynamic> matchState) {
+  bool matches(Object? object, Map<dynamic, dynamic> matchState) {
     if (object is! Path) {
       matchState[this] = 'The given object ($object) was not a Path.';
       return false;
     }
-    final Path path = object as Path;
+    final Path path = object;
     final List<String> errors = <String>[
       for (final Offset offset in includes)
         if (!path.contains(offset))
@@ -500,7 +498,7 @@ class _MismatchedCall {
   final RecordedInvocation call;
 }
 
-bool _evaluatePainter(Object object, Canvas canvas, PaintingContext context) {
+bool _evaluatePainter(Object? object, Canvas canvas, PaintingContext context) {
   if (object is _ContextPainterFunction) {
     final _ContextPainterFunction function = object;
     function(context, Offset.zero);
@@ -510,7 +508,7 @@ bool _evaluatePainter(Object object, Canvas canvas, PaintingContext context) {
   } else {
     if (object is Finder) {
       TestAsyncUtils.guardSync();
-      final Finder finder = object as Finder;
+      final Finder finder = object;
       object = finder.evaluate().single.renderObject;
     }
     if (object is RenderObject) {
@@ -525,7 +523,7 @@ bool _evaluatePainter(Object object, Canvas canvas, PaintingContext context) {
 
 abstract class _TestRecordingCanvasMatcher extends Matcher {
   @override
-  bool matches(Object object, Map<dynamic, dynamic> matchState) {
+  bool matches(Object? object, Map<dynamic, dynamic> matchState) {
     final TestRecordingCanvas canvas = TestRecordingCanvas();
     final TestRecordingPaintingContext context = TestRecordingPaintingContext(canvas);
     final StringBuffer description = StringBuffer();
@@ -630,7 +628,7 @@ class _TestRecordingCanvasPaintsNothingMatcher extends _TestRecordingCanvasMatch
 
 class _TestRecordingCanvasPaintsAssertionMatcher extends Matcher {
   @override
-  bool matches(Object object, Map<dynamic, dynamic> matchState) {
+  bool matches(Object? object, Map<dynamic, dynamic> matchState) {
     final TestRecordingCanvas canvas = TestRecordingCanvas();
     final TestRecordingPaintingContext context = TestRecordingPaintingContext(canvas);
     final StringBuffer description = StringBuffer();
@@ -686,17 +684,17 @@ class _TestRecordingCanvasPatternMatcher extends _TestRecordingCanvasMatcher imp
   }
 
   @override
-  void translate({ double x, double y }) {
+  void translate({ double? x, double? y }) {
     _predicates.add(_FunctionPaintPredicate(#translate, <dynamic>[x, y]));
   }
 
   @override
-  void scale({ double x, double y }) {
+  void scale({ double? x, double? y }) {
     _predicates.add(_FunctionPaintPredicate(#scale, <dynamic>[x, y]));
   }
 
   @override
-  void rotate({ double angle }) {
+  void rotate({ double? angle }) {
     _predicates.add(_FunctionPaintPredicate(#rotate, <dynamic>[angle]));
   }
 
@@ -716,72 +714,72 @@ class _TestRecordingCanvasPatternMatcher extends _TestRecordingCanvasMatcher imp
   }
 
   @override
-  void clipRect({ Rect rect }) {
+  void clipRect({ Rect? rect }) {
     _predicates.add(_FunctionPaintPredicate(#clipRect, <dynamic>[rect]));
   }
 
   @override
-  void clipPath({ Matcher pathMatcher }) {
+  void clipPath({ Matcher? pathMatcher }) {
     _predicates.add(_FunctionPaintPredicate(#clipPath, <dynamic>[pathMatcher]));
   }
 
   @override
-  void rect({ Rect rect, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void rect({ Rect? rect, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_RectPaintPredicate(rect: rect, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void clipRRect({ RRect rrect }) {
+  void clipRRect({ RRect? rrect }) {
     _predicates.add(_FunctionPaintPredicate(#clipRRect, <dynamic>[rrect]));
   }
 
   @override
-  void rrect({ RRect rrect, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void rrect({ RRect? rrect, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_RRectPaintPredicate(rrect: rrect, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void drrect({ RRect outer, RRect inner, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void drrect({ RRect? outer, RRect? inner, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_DRRectPaintPredicate(outer: outer, inner: inner, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void circle({ double x, double y, double radius, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void circle({ double? x, double? y, double? radius, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_CirclePaintPredicate(x: x, y: y, radius: radius, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void path({ Iterable<Offset> includes, Iterable<Offset> excludes, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void path({ Iterable<Offset>? includes, Iterable<Offset>? excludes, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_PathPaintPredicate(includes: includes, excludes: excludes, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void line({ Offset p1, Offset p2, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void line({ Offset? p1, Offset? p2, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_LinePaintPredicate(p1: p1, p2: p2, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void arc({ Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void arc({ Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_ArcPaintPredicate(color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void paragraph({ ui.Paragraph paragraph, dynamic offset }) {
+  void paragraph({ ui.Paragraph? paragraph, dynamic offset }) {
     _predicates.add(_FunctionPaintPredicate(#drawParagraph, <dynamic>[paragraph, offset]));
   }
 
   @override
-  void shadow({ Iterable<Offset> includes, Iterable<Offset> excludes, Color color, double elevation, bool transparentOccluder }) {
+  void shadow({ Iterable<Offset>? includes, Iterable<Offset>? excludes, Color? color, double? elevation, bool? transparentOccluder }) {
     _predicates.add(_ShadowPredicate(includes: includes, excludes: excludes, color: color, elevation: elevation, transparentOccluder: transparentOccluder));
   }
 
   @override
-  void image({ ui.Image image, double x, double y, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void image({ ui.Image? image, double? x, double? y, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_DrawImagePaintPredicate(image: image, x: x, y: y, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
   @override
-  void drawImageRect({ ui.Image image, Rect source, Rect destination, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+  void drawImageRect({ ui.Image? image, Rect? source, Rect? destination, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) {
     _predicates.add(_DrawImageRectPaintPredicate(image: image, source: source, destination: destination, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
   }
 
@@ -892,10 +890,10 @@ abstract class _DrawCommandPaintPredicate extends _PaintPredicate {
   final String name;
   final int argumentCount;
   final int paintArgumentIndex;
-  final Color color;
-  final double strokeWidth;
-  final bool hasMaskFilter;
-  final PaintingStyle style;
+  final Color? color;
+  final double? strokeWidth;
+  final bool? hasMaskFilter;
+  final PaintingStyle? style;
 
   String get methodName => _symbolName(symbol);
 
@@ -918,7 +916,7 @@ abstract class _DrawCommandPaintPredicate extends _PaintPredicate {
     if (strokeWidth != null && paintArgument.strokeWidth != strokeWidth)
       throw 'It called $methodName with a paint whose strokeWidth, ${paintArgument.strokeWidth}, was not exactly the expected strokeWidth ($strokeWidth).';
     if (hasMaskFilter != null && (paintArgument.maskFilter != null) != hasMaskFilter) {
-      if (hasMaskFilter)
+      if (hasMaskFilter!)
         throw 'It called $methodName with a paint that did not have a mask filter, despite expecting one.';
       else
         throw 'It called $methodName with a paint that did have a mask filter, despite not expecting one.';
@@ -945,7 +943,7 @@ abstract class _DrawCommandPaintPredicate extends _PaintPredicate {
     if (strokeWidth != null)
       description.add('strokeWidth: $strokeWidth');
     if (hasMaskFilter != null)
-      description.add(hasMaskFilter ? 'a mask filter' : 'no mask filter');
+      description.add(hasMaskFilter! ? 'a mask filter' : 'no mask filter');
     if (style != null)
       description.add('$style');
   }
@@ -955,15 +953,15 @@ class _OneParameterPaintPredicate<T> extends _DrawCommandPaintPredicate {
   _OneParameterPaintPredicate(
     Symbol symbol,
     String name, {
-    @required this.expected,
-    @required Color color,
-    @required double strokeWidth,
-    @required bool hasMaskFilter,
-    @required PaintingStyle style,
+    required this.expected,
+    required Color? color,
+    required double? strokeWidth,
+    required bool? hasMaskFilter,
+    required PaintingStyle? style,
   }) : super(
     symbol, name, 2, 1, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style);
 
-  final T expected;
+  final T? expected;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
@@ -990,18 +988,18 @@ class _TwoParameterPaintPredicate<T1, T2> extends _DrawCommandPaintPredicate {
   _TwoParameterPaintPredicate(
     Symbol symbol,
     String name, {
-    @required this.expected1,
-    @required this.expected2,
-    @required Color color,
-    @required double strokeWidth,
-    @required bool hasMaskFilter,
-    @required PaintingStyle style,
+    required this.expected1,
+    required this.expected2,
+    required Color? color,
+    required double? strokeWidth,
+    required bool? hasMaskFilter,
+    required PaintingStyle? style,
   }) : super(
     symbol, name, 3, 2, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style);
 
-  final T1 expected1;
+  final T1? expected1;
 
-  final T2 expected2;
+  final T2? expected2;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
@@ -1035,7 +1033,7 @@ class _TwoParameterPaintPredicate<T1, T2> extends _DrawCommandPaintPredicate {
 }
 
 class _RectPaintPredicate extends _OneParameterPaintPredicate<Rect> {
-  _RectPaintPredicate({ Rect rect, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _RectPaintPredicate({ Rect? rect, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawRect,
     'a rectangle',
     expected: rect,
@@ -1047,7 +1045,7 @@ class _RectPaintPredicate extends _OneParameterPaintPredicate<Rect> {
 }
 
 class _RRectPaintPredicate extends _DrawCommandPaintPredicate {
-  _RRectPaintPredicate({ this.rrect, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _RRectPaintPredicate({ this.rrect, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawRRect,
     'a rounded rectangle',
     2,
@@ -1058,7 +1056,7 @@ class _RRectPaintPredicate extends _DrawCommandPaintPredicate {
     style: style,
   );
 
-  final RRect rrect;
+  final RRect? rrect;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
@@ -1066,18 +1064,18 @@ class _RRectPaintPredicate extends _DrawCommandPaintPredicate {
     const double eps = .0001;
     final RRect actual = arguments[0] as RRect;
     if (rrect != null &&
-       ((actual.left - rrect.left).abs() > eps ||
-        (actual.right - rrect.right).abs() > eps ||
-        (actual.top - rrect.top).abs() > eps ||
-        (actual.bottom - rrect.bottom).abs() > eps ||
-        (actual.blRadiusX - rrect.blRadiusX).abs() > eps ||
-        (actual.blRadiusY - rrect.blRadiusY).abs() > eps ||
-        (actual.brRadiusX - rrect.brRadiusX).abs() > eps ||
-        (actual.brRadiusY - rrect.brRadiusY).abs() > eps ||
-        (actual.tlRadiusX - rrect.tlRadiusX).abs() > eps ||
-        (actual.tlRadiusY - rrect.tlRadiusY).abs() > eps ||
-        (actual.trRadiusX - rrect.trRadiusX).abs() > eps ||
-        (actual.trRadiusY - rrect.trRadiusY).abs() > eps)) {
+       ((actual.left - rrect!.left).abs() > eps ||
+        (actual.right - rrect!.right).abs() > eps ||
+        (actual.top - rrect!.top).abs() > eps ||
+        (actual.bottom - rrect!.bottom).abs() > eps ||
+        (actual.blRadiusX - rrect!.blRadiusX).abs() > eps ||
+        (actual.blRadiusY - rrect!.blRadiusY).abs() > eps ||
+        (actual.brRadiusX - rrect!.brRadiusX).abs() > eps ||
+        (actual.brRadiusY - rrect!.brRadiusY).abs() > eps ||
+        (actual.tlRadiusX - rrect!.tlRadiusX).abs() > eps ||
+        (actual.tlRadiusY - rrect!.tlRadiusY).abs() > eps ||
+        (actual.trRadiusX - rrect!.trRadiusX).abs() > eps ||
+        (actual.trRadiusY - rrect!.trRadiusY).abs() > eps)) {
       throw 'It called $methodName with RRect, $actual, which was not exactly the expected RRect ($rrect).';
     }
   }
@@ -1092,7 +1090,7 @@ class _RRectPaintPredicate extends _DrawCommandPaintPredicate {
 }
 
 class _DRRectPaintPredicate extends _TwoParameterPaintPredicate<RRect, RRect> {
-  _DRRectPaintPredicate({ RRect inner, RRect outer, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _DRRectPaintPredicate({ RRect? inner, RRect? outer, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawDRRect,
     'a rounded rectangle outline',
     expected1: outer,
@@ -1105,69 +1103,69 @@ class _DRRectPaintPredicate extends _TwoParameterPaintPredicate<RRect, RRect> {
 }
 
 class _CirclePaintPredicate extends _DrawCommandPaintPredicate {
-  _CirclePaintPredicate({ this.x, this.y, this.radius, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _CirclePaintPredicate({ this.x, this.y, this.radius, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawCircle, 'a circle', 3, 2, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style,
   );
 
-  final double x;
-  final double y;
-  final double radius;
+  final double? x;
+  final double? y;
+  final double? radius;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
     super.verifyArguments(arguments);
     final Offset pointArgument = arguments[0] as Offset;
     if (x != null && y != null) {
-      final Offset point = Offset(x, y);
+      final Offset point = Offset(x!, y!);
       if (point != pointArgument)
         throw 'It called $methodName with a center coordinate, $pointArgument, which was not exactly the expected coordinate ($point).';
     } else {
       if (x != null && pointArgument.dx != x)
-        throw 'It called $methodName with a center coordinate, $pointArgument, whose x-coordinate not exactly the expected coordinate (${x.toStringAsFixed(1)}).';
+        throw 'It called $methodName with a center coordinate, $pointArgument, whose x-coordinate not exactly the expected coordinate (${x!.toStringAsFixed(1)}).';
       if (y != null && pointArgument.dy != y)
-        throw 'It called $methodName with a center coordinate, $pointArgument, whose y-coordinate not exactly the expected coordinate (${y.toStringAsFixed(1)}).';
+        throw 'It called $methodName with a center coordinate, $pointArgument, whose y-coordinate not exactly the expected coordinate (${y!.toStringAsFixed(1)}).';
     }
     final double radiusArgument = arguments[1] as double;
     if (radius != null && radiusArgument != radius)
-      throw 'It called $methodName with radius, ${radiusArgument.toStringAsFixed(1)}, which was not exactly the expected radius (${radius.toStringAsFixed(1)}).';
+      throw 'It called $methodName with radius, ${radiusArgument.toStringAsFixed(1)}, which was not exactly the expected radius (${radius!.toStringAsFixed(1)}).';
   }
 
   @override
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
     if (x != null && y != null) {
-      description.add('point ${Offset(x, y)}');
+      description.add('point ${Offset(x!, y!)}');
     } else {
       if (x != null)
-        description.add('x-coordinate ${x.toStringAsFixed(1)}');
+        description.add('x-coordinate ${x!.toStringAsFixed(1)}');
       if (y != null)
-        description.add('y-coordinate ${y.toStringAsFixed(1)}');
+        description.add('y-coordinate ${y!.toStringAsFixed(1)}');
     }
     if (radius != null)
-      description.add('radius ${radius.toStringAsFixed(1)}');
+      description.add('radius ${radius!.toStringAsFixed(1)}');
   }
 }
 
 class _PathPaintPredicate extends _DrawCommandPaintPredicate {
-  _PathPaintPredicate({ this.includes, this.excludes, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _PathPaintPredicate({ this.includes, this.excludes, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawPath, 'a path', 2, 1, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style,
   );
 
-  final Iterable<Offset> includes;
-  final Iterable<Offset> excludes;
+  final Iterable<Offset>? includes;
+  final Iterable<Offset>? excludes;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
     super.verifyArguments(arguments);
     final Path pathArgument = arguments[0] as Path;
     if (includes != null) {
-      for (final Offset offset in includes) {
+      for (final Offset offset in includes!) {
         if (!pathArgument.contains(offset))
           throw 'It called $methodName with a path that unexpectedly did not contain $offset.';
       }
     }
     if (excludes != null) {
-      for (final Offset offset in excludes) {
+      for (final Offset offset in excludes!) {
         if (pathArgument.contains(offset))
           throw 'It called $methodName with a path that unexpectedly contained $offset.';
       }
@@ -1189,12 +1187,12 @@ class _PathPaintPredicate extends _DrawCommandPaintPredicate {
 
 // TODO(ianh): add arguments to test the length, angle, that kind of thing
 class _LinePaintPredicate extends _DrawCommandPaintPredicate {
-  _LinePaintPredicate({ this.p1, this.p2, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _LinePaintPredicate({ this.p1, this.p2, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawLine, 'a line', 3, 2, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style,
   );
 
-  final Offset p1;
-  final Offset p2;
+  final Offset? p1;
+  final Offset? p2;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
@@ -1222,7 +1220,7 @@ class _LinePaintPredicate extends _DrawCommandPaintPredicate {
 }
 
 class _ArcPaintPredicate extends _DrawCommandPaintPredicate {
-  _ArcPaintPredicate({ Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _ArcPaintPredicate({ Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawArc, 'an arc', 5, 4, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style,
   );
 }
@@ -1230,11 +1228,11 @@ class _ArcPaintPredicate extends _DrawCommandPaintPredicate {
 class _ShadowPredicate extends _PaintPredicate {
   _ShadowPredicate({ this.includes, this.excludes, this.color, this.elevation, this.transparentOccluder });
 
-  final Iterable<Offset> includes;
-  final Iterable<Offset> excludes;
-  final Color color;
-  final double elevation;
-  final bool transparentOccluder;
+  final Iterable<Offset>? includes;
+  final Iterable<Offset>? excludes;
+  final Color? color;
+  final double? elevation;
+  final bool? transparentOccluder;
 
   static const Symbol symbol = #drawShadow;
   String get methodName => _symbolName(symbol);
@@ -1245,13 +1243,13 @@ class _ShadowPredicate extends _PaintPredicate {
       throw 'It called $methodName with ${arguments.length} arguments; expected 4.';
     final Path pathArgument = arguments[0] as Path;
     if (includes != null) {
-      for (final Offset offset in includes) {
+      for (final Offset offset in includes!) {
         if (!pathArgument.contains(offset))
           throw 'It called $methodName with a path that unexpectedly did not contain $offset.';
       }
     }
     if (excludes != null) {
-      for (final Offset offset in excludes) {
+      for (final Offset offset in excludes!) {
         if (pathArgument.contains(offset))
           throw 'It called $methodName with a path that unexpectedly contained $offset.';
       }
@@ -1303,13 +1301,13 @@ class _ShadowPredicate extends _PaintPredicate {
 }
 
 class _DrawImagePaintPredicate extends _DrawCommandPaintPredicate {
-  _DrawImagePaintPredicate({ this.image, this.x, this.y, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _DrawImagePaintPredicate({ this.image, this.x, this.y, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawImage, 'an image', 3, 2, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style,
   );
 
-  final ui.Image image;
-  final double x;
-  final double y;
+  final ui.Image? image;
+  final double? x;
+  final double? y;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
@@ -1319,14 +1317,14 @@ class _DrawImagePaintPredicate extends _DrawCommandPaintPredicate {
       throw 'It called $methodName with an image, $imageArgument, which was not exactly the expected image ($image).';
     final Offset pointArgument = arguments[0] as Offset;
     if (x != null && y != null) {
-      final Offset point = Offset(x, y);
+      final Offset point = Offset(x!, y!);
       if (point != pointArgument)
         throw 'It called $methodName with an offset coordinate, $pointArgument, which was not exactly the expected coordinate ($point).';
     } else {
       if (x != null && pointArgument.dx != x)
-        throw 'It called $methodName with an offset coordinate, $pointArgument, whose x-coordinate not exactly the expected coordinate (${x.toStringAsFixed(1)}).';
+        throw 'It called $methodName with an offset coordinate, $pointArgument, whose x-coordinate not exactly the expected coordinate (${x!.toStringAsFixed(1)}).';
       if (y != null && pointArgument.dy != y)
-        throw 'It called $methodName with an offset coordinate, $pointArgument, whose y-coordinate not exactly the expected coordinate (${y.toStringAsFixed(1)}).';
+        throw 'It called $methodName with an offset coordinate, $pointArgument, whose y-coordinate not exactly the expected coordinate (${y!.toStringAsFixed(1)}).';
     }
   }
 
@@ -1336,24 +1334,24 @@ class _DrawImagePaintPredicate extends _DrawCommandPaintPredicate {
     if (image != null)
       description.add('image $image');
     if (x != null && y != null) {
-      description.add('point ${Offset(x, y)}');
+      description.add('point ${Offset(x!, y!)}');
     } else {
       if (x != null)
-        description.add('x-coordinate ${x.toStringAsFixed(1)}');
+        description.add('x-coordinate ${x!.toStringAsFixed(1)}');
       if (y != null)
-        description.add('y-coordinate ${y.toStringAsFixed(1)}');
+        description.add('y-coordinate ${y!.toStringAsFixed(1)}');
     }
   }
 }
 
 class _DrawImageRectPaintPredicate extends _DrawCommandPaintPredicate {
-  _DrawImageRectPaintPredicate({ this.image, this.source, this.destination, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+  _DrawImageRectPaintPredicate({ this.image, this.source, this.destination, Color? color, double? strokeWidth, bool? hasMaskFilter, PaintingStyle? style }) : super(
     #drawImageRect, 'an image', 4, 3, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style,
   );
 
-  final ui.Image image;
-  final Rect source;
-  final Rect destination;
+  final ui.Image? image;
+  final Rect? source;
+  final Rect? destination;
 
   @override
   void verifyArguments(List<dynamic> arguments) {
@@ -1500,7 +1498,7 @@ class _SaveRestorePairPaintPredicate extends _PaintPredicate {
   String toString() => 'a matching save/restore pair';
 }
 
-String _valueName(Object value) {
+String _valueName(Object? value) {
   if (value is double)
     return value.toStringAsFixed(1);
   return value.toString();
diff --git a/packages/flutter/test/rendering/mouse_tracking_test_utils.dart b/packages/flutter/test/rendering/mouse_tracking_test_utils.dart
index 423f36b2860..c122120926c 100644
--- a/packages/flutter/test/rendering/mouse_tracking_test_utils.dart
+++ b/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
diff --git a/packages/flutter/test/rendering/recording_canvas.dart b/packages/flutter/test/rendering/recording_canvas.dart
index e4956c43dbb..aae6b32e1a8 100644
--- a/packages/flutter/test/rendering/recording_canvas.dart
+++ b/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(': ');
diff --git a/packages/flutter/test/rendering/rendering_tester.dart b/packages/flutter/test/rendering/rendering_tester.dart
index 59b2a828ab7..3f5a013da19 100644
--- a/packages/flutter/test/rendering/rendering_tester.dart
+++ b/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);
diff --git a/packages/flutter/test/services/restoration.dart b/packages/flutter/test/services/restoration.dart
index a12945b4b69..0ae914da4ae 100644
--- a/packages/flutter/test/services/restoration.dart
+++ b/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) {
diff --git a/packages/flutter/test/widgets/editable_text_utils.dart b/packages/flutter/test/widgets/editable_text_utils.dart
index 0b5f0735b9a..e012fe1b835 100644
--- a/packages/flutter/test/widgets/editable_text_utils.dart
+++ b/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;
diff --git a/packages/flutter/test/widgets/gesture_utils.dart b/packages/flutter/test/widgets/gesture_utils.dart
index 528181a1342..ceef32c8ca7 100644
--- a/packages/flutter/test/widgets/gesture_utils.dart
+++ b/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';
 
diff --git a/packages/flutter/test/widgets/observer_tester.dart b/packages/flutter/test/widgets/observer_tester.dart
index 99a694ad338..f2ccbf872bd 100644
--- a/packages/flutter/test/widgets/observer_tester.dart
+++ b/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);
   }
 }
diff --git a/packages/flutter/test/widgets/restoration.dart b/packages/flutter/test/widgets/restoration.dart
index 7b82d6a4cdc..cef79725fd0 100644
--- a/packages/flutter/test/widgets/restoration.dart
+++ b/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() {
diff --git a/packages/flutter/test/widgets/semantics_tester.dart b/packages/flutter/test/widgets/semantics_tester.dart
index 2a36463a0bc..dfeb6234564 100644
--- a/packages/flutter/test/widgets/semantics_tester.dart
+++ b/packages/flutter/test/widgets/semantics_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:ui' show SemanticsFlag;
 
 import 'package:flutter/foundation.dart';
@@ -54,7 +52,7 @@ class TestSemantics {
     this.children = const <TestSemantics>[],
     this.scrollIndex,
     this.scrollChildren,
-    Iterable<SemanticsTag> tags,
+    Iterable<SemanticsTag>? tags,
   }) : assert(flags is int || flags is List<SemanticsFlag>),
        assert(actions is int || actions is List<SemanticsAction>),
        assert(label != null),
@@ -81,7 +79,7 @@ class TestSemantics {
     this.children = const <TestSemantics>[],
     this.scrollIndex,
     this.scrollChildren,
-    Iterable<SemanticsTag> tags,
+    Iterable<SemanticsTag>? tags,
   }) : id = 0,
        assert(flags is int || flags is List<SemanticsFlag>),
        assert(actions is int || actions is List<SemanticsAction>),
@@ -116,14 +114,14 @@ class TestSemantics {
     this.decreasedValue = '',
     this.textDirection,
     this.rect,
-    Matrix4 transform,
+    Matrix4? transform,
     this.elevation,
     this.thickness,
     this.textSelection,
     this.children = const <TestSemantics>[],
     this.scrollIndex,
     this.scrollChildren,
-    Iterable<SemanticsTag> tags,
+    Iterable<SemanticsTag>? tags,
   }) : assert(flags is int || flags is List<SemanticsFlag>),
        assert(actions is int || actions is List<SemanticsAction>),
        assert(label != null),
@@ -139,7 +137,7 @@ class TestSemantics {
   ///
   /// The root node has an id of zero. Other nodes are given a unique id when
   /// they are created.
-  final int id;
+  final int? id;
 
   /// The [SemanticsFlag]s set on this node.
   ///
@@ -183,7 +181,7 @@ class TestSemantics {
   /// Even if this is not set, the [hasSemantics] matcher will verify that if a
   /// label is present on the [SemanticsNode], a [SemanticsNode.textDirection]
   /// is also set.
-  final TextDirection textDirection;
+  final TextDirection? textDirection;
 
   /// The bounding box for this node in its coordinate system.
   ///
@@ -194,7 +192,7 @@ class TestSemantics {
   ///
   ///  * [TestSemantics.fullScreen] 800x600, the test screen's size in logical
   ///    pixels, useful for other full-screen widgets.
-  final Rect rect;
+  final Rect? rect;
 
   /// The test screen's size in physical pixels, typically used as the [rect]
   /// for the node with id zero.
@@ -214,7 +212,7 @@ class TestSemantics {
   /// By default, the transform is null, which represents the identity
   /// transformation (i.e., that this node has the same coordinate system as its
   /// parent).
-  final Matrix4 transform;
+  final Matrix4? transform;
 
   /// The elevation of this node relative to the parent node.
   ///
@@ -222,24 +220,24 @@ class TestSemantics {
   ///
   ///  * [SemanticsConfiguration.elevation] for a detailed discussion regarding
   ///    elevation and semantics.
-  final double elevation;
+  final double? elevation;
 
   /// The extend that this node occupies in z-direction starting at [elevation].
   ///
   /// See also:
   ///
   ///  * [SemanticsConfiguration.thickness] for a more detailed definition.
-  final double thickness;
+  final double? thickness;
 
   /// The index of the first visible semantic node within a scrollable.
-  final int scrollIndex;
+  final int? scrollIndex;
 
   /// The total number of semantic nodes within a scrollable.
-  final int scrollChildren;
+  final int? scrollChildren;
 
-  final TextSelection textSelection;
+  final TextSelection? textSelection;
 
-  static Matrix4 _applyRootChildScale(Matrix4 transform) {
+  static Matrix4 _applyRootChildScale(Matrix4? transform) {
     final Matrix4 result = Matrix4.diagonal3Values(3.0, 3.0, 1.0);
     if (transform != null)
       result.multiply(transform);
@@ -253,7 +251,7 @@ class TestSemantics {
   final Set<SemanticsTag> tags;
 
   bool _matches(
-    SemanticsNode node,
+    SemanticsNode? node,
     Map<dynamic, dynamic> matchState, {
     bool ignoreRect = false,
     bool ignoreTransform = false,
@@ -370,7 +368,7 @@ class TestSemantics {
     if (textDirection != null)
       buf.writeln('$indent  textDirection: $textDirection,');
     if (textSelection?.isValid == true)
-      buf.writeln('$indent  textSelection:\n[${textSelection.start}, ${textSelection.end}],');
+      buf.writeln('$indent  textSelection:\n[${textSelection!.start}, ${textSelection!.end}],');
     if (scrollIndex != null)
       buf.writeln('$indent scrollIndex: $scrollIndex,');
     if (rect != null)
@@ -413,7 +411,7 @@ class SemanticsTester {
 
   /// The widget tester that this object is testing the semantics of.
   final WidgetTester tester;
-  SemanticsHandle _semanticsHandle;
+  SemanticsHandle? _semanticsHandle;
 
   /// Release resources held by this semantics tester.
   ///
@@ -437,18 +435,18 @@ class SemanticsTester {
   ///
   /// If `ancestor` is not null, only the descendants of it are returned.
   Iterable<SemanticsNode> nodesWith({
-    String label,
-    String value,
-    String hint,
-    TextDirection textDirection,
-    List<SemanticsAction> actions,
-    List<SemanticsFlag> flags,
-    double scrollPosition,
-    double scrollExtentMax,
-    double scrollExtentMin,
-    int currentValueLength,
-    int maxValueLength,
-    SemanticsNode ancestor,
+    String? label,
+    String? value,
+    String? hint,
+    TextDirection? textDirection,
+    List<SemanticsAction>? actions,
+    List<SemanticsFlag>? flags,
+    double? scrollPosition,
+    double? scrollExtentMax,
+    double? scrollExtentMin,
+    int? currentValueLength,
+    int? maxValueLength,
+    SemanticsNode? ancestor,
   }) {
     bool checkNode(SemanticsNode node) {
       if (label != null && node.label != label)
@@ -497,7 +495,7 @@ class SemanticsTester {
     if (ancestor != null) {
       visit(ancestor);
     } else {
-      visit(tester.binding.pipelineOwner.semanticsOwner.rootSemanticsNode);
+      visit(tester.binding.pipelineOwner.semanticsOwner!.rootSemanticsNode!);
     }
     return result;
   }
@@ -551,7 +549,7 @@ class SemanticsTester {
   /// over-test. Prefer breaking your widgets into smaller widgets and test them
   /// individually.
   String generateTestSemanticsExpressionForCurrentSemanticsTree(DebugSemanticsDumpOrder childOrder) {
-    final SemanticsNode node = tester.binding.pipelineOwner.semanticsOwner?.rootSemanticsNode;
+    final SemanticsNode? node = tester.binding.pipelineOwner.semanticsOwner?.rootSemanticsNode;
     return _generateSemanticsTestForNode(node, 0, childOrder);
   }
 
@@ -583,7 +581,7 @@ class SemanticsTester {
 
   /// Recursively generates [TestSemantics] code for [node] and its children,
   /// indenting the expression by `indentAmount`.
-  static String _generateSemanticsTestForNode(SemanticsNode node, int indentAmount, DebugSemanticsDumpOrder childOrder) {
+  static String _generateSemanticsTestForNode(SemanticsNode? node, int indentAmount, DebugSemanticsDumpOrder childOrder) {
     if (node == null)
       return 'null';
     final String indent = '  ' * indentAmount;
@@ -594,7 +592,7 @@ class SemanticsTester {
     if (!isRoot)
       buf.writeln('  id: ${node.id},');
     if (nodeData.tags != null)
-      buf.writeln('  tags: ${_tagsToSemanticsTagExpression(nodeData.tags)},');
+      buf.writeln('  tags: ${_tagsToSemanticsTagExpression(nodeData.tags!)},');
     if (nodeData.flags != 0)
       buf.writeln('  flags: ${_flagsToSemanticsFlagExpression(nodeData.flags)},');
     if (nodeData.actions != 0)
@@ -635,10 +633,10 @@ class SemanticsTester {
 class _HasSemantics extends Matcher {
   const _HasSemantics(
     this._semantics, {
-    @required this.ignoreRect,
-    @required this.ignoreTransform,
-    @required this.ignoreId,
-    @required this.childOrder,
+    required this.ignoreRect,
+    required this.ignoreTransform,
+    required this.ignoreId,
+    required this.childOrder,
   }) : assert(_semantics != null),
        assert(ignoreRect != null),
        assert(ignoreId != null),
@@ -675,7 +673,7 @@ class _HasSemantics extends Matcher {
     return description.add('semantics node matching:\n$_semantics');
   }
 
-  String _indent(String text) {
+  String _indent(String? text) {
     return text.toString().trimRight().split('\n').map<String>((String line) => '  $line').join('\n');
   }
 
@@ -684,7 +682,7 @@ class _HasSemantics extends Matcher {
     Description result = mismatchDescription
       .add('${matchState[TestSemantics]}\n')
       .add('Current SemanticsNode tree:\n')
-      .add(_indent(RendererBinding.instance?.renderView?.debugSemantics?.toStringDeep(childOrder: childOrder)))
+      .add(_indent(RendererBinding.instance?.renderView.debugSemantics?.toStringDeep(childOrder: childOrder)))
       .add('\n')
       .add('The semantics tree would have matched the following configuration:\n')
       .add(_indent(matchState['would-match'] as String));
@@ -739,17 +737,17 @@ class _IncludesNodeWith extends Matcher {
        currentValueLength != null
      );
 
-  final String label;
-  final String value;
-  final String hint;
-  final TextDirection textDirection;
-  final List<SemanticsAction> actions;
-  final List<SemanticsFlag> flags;
-  final double scrollPosition;
-  final double scrollExtentMax;
-  final double scrollExtentMin;
-  final int currentValueLength;
-  final int maxValueLength;
+  final String? label;
+  final String? value;
+  final String? hint;
+  final TextDirection? textDirection;
+  final List<SemanticsAction>? actions;
+  final List<SemanticsFlag>? flags;
+  final double? scrollPosition;
+  final double? scrollExtentMax;
+  final double? scrollExtentMin;
+  final int? currentValueLength;
+  final int? maxValueLength;
 
   @override
   bool matches(covariant SemanticsTester item, Map<dynamic, dynamic> matchState) {
@@ -783,9 +781,9 @@ class _IncludesNodeWith extends Matcher {
       if (label != null) 'label "$label"',
       if (value != null) 'value "$value"',
       if (hint != null) 'hint "$hint"',
-      if (textDirection != null) ' (${describeEnum(textDirection)})',
-      if (actions != null) 'actions "${actions.join(', ')}"',
-      if (flags != null) 'flags "${flags.join(', ')}"',
+      if (textDirection != null) ' (${describeEnum(textDirection!)})',
+      if (actions != null) 'actions "${actions!.join(', ')}"',
+      if (flags != null) 'flags "${flags!.join(', ')}"',
       if (scrollPosition != null) 'scrollPosition "$scrollPosition"',
       if (scrollExtentMax != null) 'scrollExtentMax "$scrollExtentMax"',
       if (scrollExtentMin != null) 'scrollExtentMin "$scrollExtentMin"',
@@ -801,17 +799,17 @@ class _IncludesNodeWith extends Matcher {
 ///
 /// If null is provided for an argument, it will match against any value.
 Matcher includesNodeWith({
-  String label,
-  String value,
-  String hint,
-  TextDirection textDirection,
-  List<SemanticsAction> actions,
-  List<SemanticsFlag> flags,
-  double scrollPosition,
-  double scrollExtentMax,
-  double scrollExtentMin,
-  int maxValueLength,
-  int currentValueLength,
+  String? label,
+  String? value,
+  String? hint,
+  TextDirection? textDirection,
+  List<SemanticsAction>? actions,
+  List<SemanticsFlag>? flags,
+  double? scrollPosition,
+  double? scrollExtentMax,
+  double? scrollExtentMin,
+  int? maxValueLength,
+  int? currentValueLength,
 }) {
   return _IncludesNodeWith(
     label: label,
diff --git a/packages/flutter/test/widgets/states.dart b/packages/flutter/test/widgets/states.dart
index 76064a6cb98..02d38fea48a 100644
--- a/packages/flutter/test/widgets/states.dart
+++ b/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',
diff --git a/packages/flutter/test/widgets/test_border.dart b/packages/flutter/test/widgets/test_border.dart
index 26b9dac888f..51923eb1a92 100644
--- a/packages/flutter/test/widgets/test_border.dart
+++ b/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');
   }
 }
diff --git a/packages/flutter/test/widgets/test_widgets.dart b/packages/flutter/test/widgets/test_widgets.dart
index 3ec1db94969..518d43f9490 100644
--- a/packages/flutter/test/widgets/test_widgets.dart
+++ b/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;
diff --git a/packages/flutter/test/widgets/text.dart b/packages/flutter/test/widgets/text.dart
index deb8bde7866..4ccca393ae5 100644
--- a/packages/flutter/test/widgets/text.dart
+++ b/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;
diff --git a/packages/flutter/test/widgets/widget_inspector_test_utils.dart b/packages/flutter/test/widgets/widget_inspector_test_utils.dart
index 3ce8dd4b921..be12aed1b99 100644
--- a/packages/flutter/test/widgets/widget_inspector_test_utils.dart
+++ b/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!);
     }
   }
 }