Add doc and test for Container's hitTest behavior (#57522)

packages/flutter/lib/src/widgets/container.dart

@@ -184,6 +184,11 @@ class DecoratedBox extends SingleChildRenderObjectWidget {
 /// `width`, `height`, and [constraints] arguments to the constructor override
 /// this.
 ///
+/// By default, containers return false for all hit tests. If the [color]
+/// property is specified, the hit testing is handled by [ColoredBox], which
+/// always returns true. If the [decoration] or [foregroundDecoration] properties
+/// are specified, hit testing is handled by [Decoration.hitTest].
+///
 /// ## Layout behavior
 ///
 /// _See [BoxConstraints] for an introduction to box layout models._

packages/flutter/test/widgets/container_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 import 'package:mockito/mockito.dart';
@@ -502,6 +503,60 @@ void main() {
       findsOneWidget,
     );
   });
+
+  testWidgets('Container is hittable only when having decorations', (WidgetTester tester) async {
+    bool tapped = false;
+    await tester.pumpWidget(GestureDetector(
+      onTap: () { tapped = true; },
+      child: Container(
+        decoration: const BoxDecoration(color: Colors.black),
+      ),
+    ));
+
+    await tester.tap(find.byType(Container));
+    expect(tapped, true);
+    tapped = false;
+
+    await tester.pumpWidget(GestureDetector(
+      onTap: () { tapped = true; },
+      child: Container(
+        foregroundDecoration: const BoxDecoration(color: Colors.black),
+      ),
+    ));
+
+    await tester.tap(find.byType(Container));
+    expect(tapped, true);
+    tapped = false;
+
+    await tester.pumpWidget(GestureDetector(
+      onTap: () { tapped = true; },
+      child: Container(
+        color: Colors.black,
+      ),
+    ));
+
+    await tester.tap(find.byType(Container));
+    expect(tapped, true);
+    tapped = false;
+
+    // Everything but color or decorations
+    await tester.pumpWidget(GestureDetector(
+      onTap: () { tapped = true; },
+      child: Center(
+        child: Container(
+          alignment: Alignment.bottomRight,
+          padding: const EdgeInsets.all(2),
+          width: 50,
+          height: 50,
+          margin: const EdgeInsets.all(2),
+          transform: Matrix4.rotationZ(1),
+        ),
+      ),
+    ));
+
+    await tester.tap(find.byType(Container));
+    expect(tapped, false);
+  });
 }
 
 class _MockPaintingContext extends Mock implements PaintingContext {}