new_contents: from django.urls import reverse
  from rest_framework import status
  
  from dcim.models import Region, Site
  from ipam.models import VLAN
  from utilities.testing import APITestCase
  
  
  class WritableNestedSerializerTest(APITestCase):
      """
      Test the operation of WritableNestedSerializer using VLANSerializer as our test subject.
      """
  
      def setUp(self):
  
          super().setUp()
  
          self.region_a = Region.objects.create(name='Region A', slug='region-a')
          self.site1 = Site.objects.create(region=self.region_a, name='Site 1', slug='site-1')
          self.site2 = Site.objects.create(region=self.region_a, name='Site 2', slug='site-2')
  
      def test_related_by_pk(self):
  
          data = {
              'vid': 100,
              'name': 'Test VLAN 100',
              'site': self.site1.pk,
          }
  
          url = reverse('ipam-api:vlan-list')
          response = self.client.post(url, data, format='json', **self.header)
  
          self.assertHttpStatus(response, status.HTTP_201_CREATED)
          self.assertEqual(response.data['site']['id'], self.site1.pk)
          vlan = VLAN.objects.get(pk=response.data['id'])
          self.assertEqual(vlan.site, self.site1)
  
      def test_related_by_pk_no_match(self):
  
          data = {
              'vid': 100,
              'name': 'Test VLAN 100',
              'site': 999,
          }
  
          url = reverse('ipam-api:vlan-list')
          response = self.client.post(url, data, format='json', **self.header)
  
          self.assertHttpStatus(response, status.HTTP_400_BAD_REQUEST)
          self.assertEqual(VLAN.objects.count(), 0)
          self.assertTrue(response.data['site'][0].startswith("Related object not found"))
  
      def test_related_by_attributes(self):
  
          data = {
              'vid': 100,
              'name': 'Test VLAN 100',
              'site': {
                  'name': 'Site 1'
              },
          }
  
          url = reverse('ipam-api:vlan-list')
          response = self.client.post(url, data, format='json', **self.header)
  
          self.assertHttpStatus(response, status.HTTP_201_CREATED)
          self.assertEqual(response.data['site']['id'], self.site1.pk)
          vlan = VLAN.objects.get(pk=response.data['id'])
          self.assertEqual(vlan.site, self.site1)
  
      def test_related_by_attributes_no_match(self):
  
          data = {
              'vid': 100,
              'name': 'Test VLAN 100',
              'site': {
                  'name': 'Site X'
              },
          }
  
          url = reverse('ipam-api:vlan-list')
          response = self.client.post(url, data, format='json', **self.header)
  
          self.assertHttpStatus(response, status.HTTP_400_BAD_REQUEST)
          self.assertEqual(VLAN.objects.count(), 0)
          self.assertTrue(response.data['site'][0].startswith("Related object not found"))
  
      def test_related_by_attributes_multiple_matches(self):
  
          data = {
              'vid': 100,
              'name': 'Test VLAN 100',
              'site': {
                  'region': {
                      "name": "Region A",
                  },
              },
          }
  
          url = reverse('ipam-api:vlan-list')
          response = self.client.post(url, data, format='json', **self.header)
  
          self.assertHttpStatus(response, status.HTTP_400_BAD_REQUEST)
          self.assertEqual(VLAN.objects.count(), 0)
          self.assertTrue(response.data['site'][0].startswith("Multiple objects match"))
  
      def test_related_by_invalid(self):
  
          data = {
              'vid': 100,
              'name': 'Test VLAN 100',
              'site': 'XXX',
          }
  
          url = reverse('ipam-api:vlan-list')
          response = self.client.post(url, data, format='json', **self.header)
  
          self.assertHttpStatus(response, status.HTTP_400_BAD_REQUEST)
          self.assertEqual(VLAN.objects.count(), 0)
  
subject: Add tests for WritableNestedSerializer