Make it easier to ensure semantics in widgetTests (#29387)

* Make it easier to ensure semantics

packages/flutter_test/lib/src/widget_tester.dart

diff --git a/packages/flutter_test/lib/src/widget_tester.dart b/packages/flutter_test/lib/src/widget_tester.dart
index 0b79c24..9063cc1 100644
--- a/packages/flutter_test/lib/src/widget_tester.dart
+++ b/packages/flutter_test/lib/src/widget_tester.dart
@@ -58,6 +58,11 @@
 /// is defined by the timeout property,
 /// which defaults to [TestWidgetsFlutterBinding.defaultTestTimeout].
 ///
+/// If the `enableSemantics` parameter is set to `true`,
+/// [WidgetTester.ensureSemantics] will have been called before the tester is
+/// passed to the `callback`, and that handle will automatically be disposed
+/// after the callback is finished.
+///
 /// This function uses the [test] function in the test package to
 /// register the given callback as a test. The callback, when run,
 /// will be given a new instance of [WidgetTester]. The [find] object
@@ -84,6 +89,7 @@
   WidgetTesterCallback callback, {
   bool skip = false,
   test_package.Timeout timeout,
+  bool semanticsEnabled = false,
 }) {
   final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   final WidgetTester tester = WidgetTester._(binding);
@@ -91,10 +97,17 @@
   test(
     description,
     () {
+      SemanticsHandle semanticsHandle;
+      if (semanticsEnabled == true) {
+        semanticsHandle = tester.ensureSemantics();
+      }
       tester._recordNumberOfSemanticsHandles();
       test_package.addTearDown(binding.postTest);
       return binding.runTest(
-        () => callback(tester),
+        () async {
+          await callback(tester);
+          semanticsHandle?.dispose();
+        },
         tester._endOfTestVerifications,
         description: description ?? '',
       );

packages/flutter_test/test/widget_tester_test.dart

diff --git a/packages/flutter_test/test/widget_tester_test.dart b/packages/flutter_test/test/widget_tester_test.dart
index 2137652..0d54203 100644
--- a/packages/flutter_test/test/widget_tester_test.dart
+++ b/packages/flutter_test/test/widget_tester_test.dart
@@ -589,6 +589,27 @@
       semanticsHandle.dispose();
     });
 
+    testWidgets('Can enable semantics for tests via semanticsEnabled', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: Container(
+              child: OutlineButton(
+                  onPressed: () { },
+                  child: const Text('hello'),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      final SemanticsNode node = tester.getSemantics(find.text('hello'));
+      final SemanticsData semantics = node.getSemanticsData();
+      expect(semantics.label, 'hello');
+      expect(semantics.hasAction(SemanticsAction.tap), true);
+      expect(semantics.hasFlag(SemanticsFlag.isButton), true);
+    }, semanticsEnabled: true);
+
     testWidgets('Returns merged SemanticsData', (WidgetTester tester) async {
       final SemanticsHandle semanticsHandle = tester.ensureSemantics();
       const Key key = Key('test');