Migrate Switch tests to null safety. (#68133)

packages/flutter/lib/src/material/switch.dart

@@ -149,7 +149,7 @@ class Switch extends StatefulWidget {
   ///   },
   /// )
   /// ```
-  final ValueChanged<bool?>? onChanged;
+  final ValueChanged<bool>? onChanged;
 
   /// The color to use when this switch is on.
   ///
@@ -440,7 +440,7 @@ class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
   final Color activeTrackColor;
   final Color inactiveTrackColor;
   final ImageConfiguration configuration;
-  final ValueChanged<bool?>? onChanged;
+  final ValueChanged<bool>? onChanged;
   final BoxConstraints additionalConstraints;
   final DragStartBehavior dragStartBehavior;
   final bool hasFocus;
@@ -463,7 +463,7 @@ class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
       activeTrackColor: activeTrackColor,
       inactiveTrackColor: inactiveTrackColor,
       configuration: configuration,
-      onChanged: onChanged,
+      onChanged: onChanged != null ? _handleValueChanged : null,
       textDirection: Directionality.of(context)!,
       additionalConstraints: additionalConstraints,
       hasFocus: hasFocus,
@@ -487,7 +487,7 @@ class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
       ..activeTrackColor = activeTrackColor
       ..inactiveTrackColor = inactiveTrackColor
       ..configuration = configuration
-      ..onChanged = onChanged
+      ..onChanged = onChanged != null ? _handleValueChanged : null
       ..textDirection = Directionality.of(context)!
       ..additionalConstraints = additionalConstraints
       ..dragStartBehavior = dragStartBehavior
@@ -495,6 +495,17 @@ class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
       ..hovering = hovering
       ..vsync = state;
   }
+
+  void _handleValueChanged(bool? value) {
+    // Wrap the onChanged callback because the RenderToggleable supports tri-state
+    // values (i.e. value can be null), but the Switch doesn't. We pass false
+    // for the tristate param to RenderToggleable, so value should never
+    // be null.
+    assert(value != null);
+    if (onChanged != null) {
+      onChanged!(value!);
+    }
+  }
 }
 
 class _RenderSwitch extends RenderToggleable {
@@ -650,7 +661,6 @@ class _RenderSwitch extends RenderToggleable {
     }
   }
 
-
   @override
   void detach() {
     _cachedThumbPainter?.dispose();

packages/flutter/lib/src/material/switch_list_tile.dart

@@ -346,7 +346,7 @@ class SwitchListTile extends StatelessWidget {
   ///   title: Text('Selection'),
   /// )
   /// ```
-  final ValueChanged<bool?>? onChanged;
+  final ValueChanged<bool>? onChanged;
 
   /// The color to use when this switch is on.
   ///

packages/flutter/test/material/switch_list_tile_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/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
@@ -12,7 +10,7 @@ import '../rendering/mock_canvas.dart';
 
 import '../widgets/semantics_tester.dart';
 
-Widget wrap({ Widget child }) {
+Widget wrap({ required Widget child }) {
   return MediaQuery(
     data: const MediaQueryData(),
     child: Directionality(
@@ -51,14 +49,14 @@ void main() {
           ),
           CheckboxListTile(
             value: true,
-            onChanged: (bool value) { },
+            onChanged: (bool? value) { },
             title: const Text('BBB'),
             secondary: const Text('bbb'),
           ),
           RadioListTile<bool>(
             value: true,
             groupValue: false,
-            onChanged: (bool value) { },
+            onChanged: (bool? value) { },
             title: const Text('CCC'),
             secondary: const Text('ccc'),
           ),
@@ -278,7 +276,7 @@ void main() {
     );
 
     await tester.pump();
-    expect(Focus.of(childKey.currentContext, nullOk: true).hasPrimaryFocus, isTrue);
+    expect(Focus.of(childKey.currentContext!)!.hasPrimaryFocus, isTrue);
 
     await tester.pumpWidget(
       MaterialApp(
@@ -298,7 +296,7 @@ void main() {
     );
 
     await tester.pump();
-    expect(Focus.of(childKey.currentContext, nullOk: true).hasPrimaryFocus, isFalse);
+    expect(Focus.of(childKey.currentContext!)!.hasPrimaryFocus, isFalse);
   });
 
   testWidgets('SwitchListTile controlAffinity test', (WidgetTester tester) async {

packages/flutter/test/material/switch_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/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -318,7 +316,7 @@ void main() {
         Material.of(tester.element(find.byType(Switch))),
         paints
           ..rrect(
-              color: Colors.blue[600].withAlpha(0x80),
+              color: Colors.blue[600]!.withAlpha(0x80),
               rrect: RRect.fromLTRBR(
                   383.5, 293.0, 416.5, 307.0, const Radius.circular(7.0)))
           ..circle(color: const Color(0x33000000))
@@ -608,10 +606,10 @@ void main() {
     expect(value, true);
     expect(semanticEvent, <String, dynamic>{
       'type': 'tap',
-      'nodeId': object.debugSemantics.id,
+      'nodeId': object.debugSemantics!.id,
       'data': <String, dynamic>{},
     });
-    expect(object.debugSemantics.getSemanticsData().hasAction(SemanticsAction.tap), true);
+    expect(object.debugSemantics!.getSemanticsData().hasAction(SemanticsAction.tap), true);
 
     semanticsTester.dispose();
     SystemChannels.accessibility.setMockMessageHandler(null);
@@ -658,10 +656,10 @@ void main() {
     expect(value, true);
     expect(semanticEvent, <String, dynamic>{
       'type': 'tap',
-      'nodeId': object.debugSemantics.id,
+      'nodeId': object.debugSemantics!.id,
       'data': <String, dynamic>{},
     });
-    expect(object.debugSemantics.getSemanticsData().hasAction(SemanticsAction.tap), true);
+    expect(object.debugSemantics!.getSemanticsData().hasAction(SemanticsAction.tap), true);
 
     semanticsTester.dispose();
     SystemChannels.accessibility.setMockMessageHandler(null);
@@ -943,7 +941,7 @@ void main() {
 
     await tester.pump();
 
-    expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.text);
+    expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.text);
 
     // Test Switch() constructor
     await tester.pumpWidget(
@@ -967,7 +965,7 @@ void main() {
     );
 
     await gesture.moveTo(tester.getCenter(find.byType(Switch)));
-    expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.text);
+    expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.text);
 
     // Test default cursor
     await tester.pumpWidget(
@@ -989,7 +987,7 @@ void main() {
       ),
     );
 
-    expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.click);
+    expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.click);
 
     // Test default cursor when disabled
     await tester.pumpWidget(
@@ -1011,7 +1009,7 @@ void main() {
       ),
     );
 
-    expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.basic);
+    expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.basic);
 
     await tester.pumpAndSettle();
   });
@@ -1020,7 +1018,7 @@ void main() {
     // Regression test for https://github.com/flutter/flutter/issues/61247.
     bool value = true;
     bool enabled = true;
-    StateSetter stateSetter;
+    late StateSetter stateSetter;
     await tester.pumpWidget(
       Directionality(
         textDirection: TextDirection.ltr,