feat(tests): updated tests coverage to 66.5%

test/features/registration_v2/models/registration_model_test.dart

@@ -80,5 +80,35 @@ void main() {
       expect(model.weight, 80);
       expect(model.height, 175);
     });
+
+    test('toJson serializes RegistrationModel correctly', () {
+      final model = RegistrationModel(
+        firstName: 'John',
+        lastName: 'Doe',
+        email: 'john.doe@example.com',
+        phone: '+1234567890',
+        gender: 'male',
+        password: 'password123',
+        confirmPassword: 'password123',
+        weight: 75,
+        height: 180,
+        activityCoefficient: 1.5,
+        birthday: '1990-01-01',
+      );
+
+      final json = model.toJson();
+
+      expect(json['first_name'], 'John');
+      expect(json['last_name'], 'Doe');
+      expect(json['email'], 'john.doe@example.com');
+      expect(json['phone'], '+1234567890');
+      expect(json['gender'], 'male');
+      expect(json['password'], 'password123');
+      expect(json['password_confirmation'], 'password123');
+      expect(json['weight'], 75);
+      expect(json['height'], 180);
+      expect(json['activity_coefficient'], 1.5);
+      expect(json['birthdate'], '1990-01-01');
+    });
   });
 }