Add E2E test for test case display empty view for favorite folder

integration_test/scenarios/mailbox/display_empty_view_for_favorite_folder_scenario.dart

@@ -0,0 +1,37 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tmail_ui_user/features/mailbox/presentation/widgets/label_mailbox_item_widget.dart';
+import 'package:tmail_ui_user/features/mailbox/presentation/widgets/mailbox_item_widget.dart';
+import 'package:tmail_ui_user/main/localizations/app_localizations.dart';
+
+import '../../base/base_test_scenario.dart';
+import '../../robots/mailbox_menu_robot.dart';
+import '../../robots/thread_robot.dart';
+
+class DisplayEmptyViewForFavoriteFolderScenario extends BaseTestScenario {
+  const DisplayEmptyViewForFavoriteFolderScenario(super.$);
+
+  @override
+  Future<void> runTestLogic() async {
+    final threadRobot = ThreadRobot($);
+    final mailboxMenuRobot = MailboxMenuRobot($);
+    final appLocalizations = AppLocalizations();
+
+    await threadRobot.openMailbox();
+    await _expectFolderVisible(appLocalizations.favoriteMailboxDisplayName);
+
+    await mailboxMenuRobot.openFolderByName(
+      appLocalizations.favoriteMailboxDisplayName,
+    );
+    await $.pumpAndTrySettle();
+    await _expectEmptyViewVisible();
+  }
+
+  Future<void> _expectFolderVisible(String folderName) {
+    return expectViewVisible($(MailboxItemWidget)
+        .$(LabelMailboxItemWidget)
+        .$(find.text(folderName)));
+  }
+
+  Future<void> _expectEmptyViewVisible() =>
+      expectViewVisible($(#empty_thread_view));
+}

integration_test/tests/mailbox/display_empty_view_for_favorite_folder_test.dart

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+import '../../base/test_base.dart';
+import '../../scenarios/mailbox/display_empty_view_for_favorite_folder_scenario.dart';
+
+void main() {
+  TestBase().runPatrolTest(
+    description: 'Should display empty view when no mail favorites',
+    scenarioBuilder: ($) => DisplayEmptyViewForFavoriteFolderScenario($),
+  );
+}