Another context menus example: custom menu (#1577)

experimental/context_menus/test/cascading_menu_page_test.dart

@@ -14,7 +14,7 @@ void main() {
     await tester.dragUntilVisible(
       find.text(CascadingMenuPage.title),
       find.byType(ListView),
-      const Offset(0.0, -300.0),
+      const Offset(0.0, -250.0),
     );
     await tester.tap(find.text(CascadingMenuPage.title));
     await tester.pumpAndSettle();

experimental/context_menus/test/custom_menu_page_test.dart

@@ -0,0 +1,58 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:context_menus/main.dart';
+import 'package:context_menus/custom_menu_page.dart';
+
+void main() {
+  testWidgets('Shows default buttons in a custom context menu',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(const MyApp());
+
+    // Navigate to the CustomMenuPage example.
+    await tester.dragUntilVisible(
+      find.text(CustomMenuPage.title),
+      find.byType(ListView),
+      const Offset(0.0, -200.0),
+    );
+    await tester.tap(find.text(CustomMenuPage.title));
+    await tester.pumpAndSettle();
+
+    // Right click on the text field to show the context menu.
+    final TestGesture gesture = await tester.startGesture(
+      tester.getCenter(find.byType(EditableText)),
+      kind: PointerDeviceKind.mouse,
+      buttons: kSecondaryMouseButton,
+    );
+    await tester.pump();
+    await gesture.up();
+    await gesture.removePointer();
+    await tester.pumpAndSettle();
+
+    // A custom context menu is shown, and the buttons are the default ones.
+    expect(find.byType(AdaptiveTextSelectionToolbar), findsNothing);
+    expect(find.byType(CupertinoAdaptiveTextSelectionToolbar), findsNothing);
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.iOS:
+        expect(
+            find.byType(CupertinoTextSelectionToolbarButton), findsNWidgets(2));
+        break;
+      case TargetPlatform.macOS:
+        expect(find.byType(CupertinoDesktopTextSelectionToolbarButton),
+            findsNWidgets(2));
+        break;
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+        expect(find.byType(TextSelectionToolbarTextButton), findsNWidgets(1));
+        break;
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        expect(
+            find.byType(DesktopTextSelectionToolbarButton), findsNWidgets(1));
+        break;
+    }
+  });
+}