Do not return partial semantics from tester.getSemantics (flutter#60367)

Author: goderbauer

packages/flutter_test/lib/src/widget_tester.dart

@@ -997,6 +997,11 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
   /// The ancestor's semantic data will include the child's as well as
   /// other nodes that have been merged together.
   ///
+  /// If the [SemanticsNode] of the object identified by the finder is
+  /// force-merged into an ancestor (e.g. via the [MergeSemantics] widget)
+  /// the node into which it is merged is returned. That node will include
+  /// all the semantics information of the nodes merged into it.
+  ///
   /// Will throw a [StateError] if the finder returns more than one element or
   /// if no semantics are found or are not enabled.
   SemanticsNode getSemantics(Finder finder) {
@@ -1012,7 +1017,7 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
     final Element element = candidates.single;
     RenderObject renderObject = element.findRenderObject();
     SemanticsNode result = renderObject.debugSemantics;
-    while (renderObject != null && result == null) {
+    while (renderObject != null && (result == null || result.isMergedIntoParent)) {
       renderObject = renderObject?.parent as RenderObject;
       result = renderObject?.debugSemantics;
     }

packages/flutter_test/test/widget_tester_test.dart

@@ -127,6 +127,34 @@ void main() {
       expect(semantics.label, 'A\nB\nC');
       semanticsHandle.dispose();
     });
+
+    testWidgets('Does not return partial semantics', (WidgetTester tester) async {
+      final SemanticsHandle semanticsHandle = tester.ensureSemantics();
+      final Key key = UniqueKey();
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: MergeSemantics(
+              child: Semantics(
+                container: true,
+                label: 'A',
+                child: Semantics(
+                  container: true,
+                  key: key,
+                  label: 'B',
+                  child: Container(),
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      final SemanticsNode node = tester.getSemantics(find.byKey(key));
+      final SemanticsData semantics = node.getSemanticsData();
+      expect(semantics.label, 'A\nB');
+      semanticsHandle.dispose();
+    });
   });
 
   group('ensureVisible', () {