Migrate more tests (#68037)

* Migrate more tests

* fix

packages/flutter/test/widgets/multichild_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -18,12 +16,12 @@ void checkTree(WidgetTester tester, List<BoxDecoration> expectedDecorations) {
   expect(element.renderObject, isA<RenderStack>());
   final RenderStack renderObject = element.renderObject as RenderStack;
   try {
-    RenderObject child = renderObject.firstChild;
+    RenderObject? child = renderObject.firstChild;
     for (final BoxDecoration decoration in expectedDecorations) {
       expect(child, isA<RenderDecoratedBox>());
-      final RenderDecoratedBox decoratedBox = child as RenderDecoratedBox;
+      final RenderDecoratedBox decoratedBox = child! as RenderDecoratedBox;
       expect(decoratedBox.decoration, equals(decoration));
-      final StackParentData decoratedBoxParentData = decoratedBox.parentData as StackParentData;
+      final StackParentData decoratedBoxParentData = decoratedBox.parentData! as StackParentData;
       child = decoratedBoxParentData.nextSibling;
     }
     expect(child, isNull);
@@ -34,10 +32,13 @@ void checkTree(WidgetTester tester, List<BoxDecoration> expectedDecorations) {
 }
 
 class MockMultiChildRenderObjectWidget extends MultiChildRenderObjectWidget {
-  MockMultiChildRenderObjectWidget({ Key key, List<Widget> children }) : super(key: key, children: children);
+  MockMultiChildRenderObjectWidget({ Key? key, required List<Widget> children }) : super(key: key, children: children);
 
   @override
-  RenderObject createRenderObject(BuildContext context) => null;
+  RenderObject createRenderObject(BuildContext context) {
+    assert(false);
+    return FakeRenderObject();
+  }
 }
 
 void main() {
@@ -354,17 +355,11 @@ void main() {
 
     checkTree(tester, <BoxDecoration>[kBoxDecorationB, kBoxDecorationC]);
   });
+}
 
-  // Regression test for https://github.com/flutter/flutter/issues/37136.
-  test('provides useful assertion message when one of the children is null', () {
-    bool assertionTriggered = false;
-    try {
-      MockMultiChildRenderObjectWidget(children: const <Widget>[null]);
-    } catch (e) {
-      expect(e.toString(), contains("MockMultiChildRenderObjectWidget's children must not contain any null values,"));
-      assertionTriggered = true;
-    }
-
-    expect(assertionTriggered, isTrue);
-  });
+class FakeRenderObject extends RenderBox {
+  @override
+  void performLayout() {
+    size = constraints.biggest;
+  }
 }

packages/flutter/test/widgets/multichildobject_with_keys_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -68,7 +66,7 @@ void main() {
 List<String> _getChildOrder(RenderFlex flex) {
   final List<String> childOrder = <String>[];
   flex.visitChildren((RenderObject child) {
-    childOrder.add(((child as RenderParagraph).text as TextSpan).text);
+    childOrder.add(((child as RenderParagraph).text as TextSpan).text!);
   });
   return childOrder;
 }

packages/flutter/test/widgets/navigator_and_layers_test.dart

@@ -2,15 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 
 import 'test_widgets.dart';
 
 class TestCustomPainter extends CustomPainter {
-  TestCustomPainter({ this.log, this.name });
+  TestCustomPainter({ required this.log, required this.name });
 
   final List<String> log;
   final String name;

packages/flutter/test/widgets/navigator_replacement_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 
@@ -60,11 +58,11 @@ void main() {
       final NavigatorState navigator = tester.state(find.byType(Navigator));
       final List<String> log = <String>[];
       observer
-        ..onPushed = (Route<dynamic> route, Route<dynamic> previousRoute) {
-          log.add('${route.settings.name} pushed, previous route: ${previousRoute.settings.name}');
+        ..onPushed = (Route<dynamic>? route, Route<dynamic>? previousRoute) {
+          log.add('${route!.settings.name} pushed, previous route: ${previousRoute!.settings.name}');
         }
-        ..onRemoved = (Route<dynamic> route, Route<dynamic> previousRoute) {
-          log.add('${route.settings.name} removed, previous route: ${previousRoute?.settings?.name}');
+        ..onRemoved = (Route<dynamic>? route, Route<dynamic>? previousRoute) {
+          log.add('${route!.settings.name} removed, previous route: ${previousRoute?.settings.name}');
         };
 
 

packages/flutter/test/widgets/notification_test.dart

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

packages/flutter/test/widgets/obscured_animated_image_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:typed_data';
 import 'dart:ui' as ui show Image;
 
@@ -30,21 +28,20 @@ Future<void> main() async {
       ),
     );
     final RenderImage renderImage = tester.renderObject(find.byType(Image));
-    final ui.Image image1 = renderImage.image;
+    final ui.Image? image1 = renderImage.image;
     await tester.pump(const Duration(milliseconds: 100));
-    final ui.Image image2 = renderImage.image;
+    final ui.Image? image2 = renderImage.image;
     expect(image1, isNot(same(image2)));
 
-
-    Navigator.pushNamed(imageKey.currentContext, '/page');
+    Navigator.pushNamed(imageKey.currentContext!, '/page');
     await tester.pump(); // Starts the page animation.
     await tester.pump(const Duration(seconds: 1)); // Let the page animation complete.
 
     // The image is now obscured by another page, it should not be changing
     // frames.
-    final ui.Image image3 = renderImage.image;
+    final ui.Image? image3 = renderImage.image;
     await tester.pump(const Duration(milliseconds: 100));
-    final ui.Image image4 = renderImage.image;
+    final ui.Image? image4 = renderImage.image;
     expect(image3, same(image4));
   });
 }

packages/flutter/test/widgets/opacity_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
@@ -191,7 +189,7 @@ void main() {
     final Element element = find.byType(RepaintBoundary).first.evaluate().single;
     // The following line will send the layer to engine and cause crash if an
     // empty opacity layer is sent.
-    final OffsetLayer offsetLayer = element.renderObject.debugLayer as OffsetLayer;
+    final OffsetLayer offsetLayer = element.renderObject!.debugLayer! as OffsetLayer;
     await offsetLayer.toImage(const Rect.fromLTRB(0.0, 0.0, 1.0, 1.0));
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/42767
 }

packages/flutter/test/widgets/overflow_bar_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 
@@ -52,7 +50,7 @@ void main() {
     final Key child2Key = UniqueKey();
     final Key child3Key = UniqueKey();
 
-    Widget buildFrame({ double spacing, TextDirection textDirection }) {
+    Widget buildFrame({ required double spacing, required TextDirection textDirection }) {
       return Directionality(
         textDirection: textDirection,
         child: Align(
@@ -176,7 +174,7 @@ void main() {
   });
 
   testWidgets('OverflowBar intrinsic width', (WidgetTester tester) async {
-    Widget buildFrame({ double width }) {
+    Widget buildFrame({ required double width }) {
       return Directionality(
         textDirection: TextDirection.ltr,
         child: Center(
@@ -207,7 +205,7 @@ void main() {
   });
 
   testWidgets('OverflowBar intrinsic height', (WidgetTester tester) async {
-    Widget buildFrame({ double maxWidth }) {
+    Widget buildFrame({ required double maxWidth }) {
       return Directionality(
         textDirection: TextDirection.ltr,
         child: Center(