test: add unit tests for ValidationUtils covering email, phone, URL, password, username, text, title, and description length validations, along with phone normalization and error message generation.

test/core/utils/validation_utils_test.dart

@@ -30,6 +30,28 @@ void main() {
       });
     });
 
+    group('normalizePhone', () {
+      test('normalizes phone starting with +7', () {
+        expect(ValidationUtils.normalizePhone('+7 (915) 062 61 51'), '+79150626151');
+      });
+
+      test('normalizes phone starting with 8', () {
+        expect(ValidationUtils.normalizePhone('89150626151'), '+79150626151');
+      });
+
+      test('normalizes 10-digit phone', () {
+        expect(ValidationUtils.normalizePhone('9150626151'), '+79150626151');
+      });
+
+      test('returns empty string for empty input', () {
+        expect(ValidationUtils.normalizePhone(''), '');
+      });
+
+      test('returns empty string for input with no digits', () {
+        expect(ValidationUtils.normalizePhone('abc'), '');
+      });
+    });
+
     group('isValidUrl', () {
       test('returns true for valid URL', () {
         expect(ValidationUtils.isValidUrl('https://example.com'), isTrue);