TF-2517 Fix rename/create a folder with special characters do not show error message

test/features/mailbox/presentation/utils/mailbox_name_special_character_validator_test.dart

@@ -0,0 +1,39 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tmail_ui_user/features/mailbox_creator/domain/extensions/mailbox_name_special_character_validator_extension.dart';
+
+void main() {
+  group('isValid::test', () {
+
+    test('should return true for a valid string', () {
+      expect('hello'.isValid, isTrue);
+    });
+
+    test('should return false for a string starting with #', () {
+      expect('#hello'.isValid, isFalse);
+    });
+
+    test('should return false for a string containing %', () {
+      expect('hello%world'.isValid, isFalse);
+    });
+
+    test('should return false for a string containing *', () {
+      expect('hello*world'.isValid, isFalse);
+    });
+
+    test('should return false for a string containing \\n', () {
+      expect('hello\nworld'.isValid, isFalse);
+    });
+
+    test('should return false for a string containing \\r', () {
+      expect('hello\rworld'.isValid, isFalse);
+    });
+
+    test('should return true for an empty string', () {
+      expect(''.isValid, isTrue);
+    });
+
+    test('should return true for a string with no forbidden characters and not starting with #', () {
+      expect('validString123'.isValid, isTrue);
+    });
+  });
+}