Test dns_assignment with external dns integration

After the ports dns_assignment attribute calculation was changed by [1]
to implement [2], this patch updates the corresponding scenario test
case to reflect the current functionality

[1] https://review.opendev.org/c/openstack/neutron/+/731624/
[2] https://specs.openstack.org/openstack//neutron-specs/specs/victoria/port_dns_assignment.html

Change-Id: If667550a8745ea224d2099d662dd901dc5368ae5
Closes-Bug: #1956632
diff --git a/neutron_tempest_plugin/scenario/test_dns_integration.py b/neutron_tempest_plugin/scenario/test_dns_integration.py
index 240a5a8..6f2756c 100644
--- a/neutron_tempest_plugin/scenario/test_dns_integration.py
+++ b/neutron_tempest_plugin/scenario/test_dns_integration.py
@@ -147,11 +147,16 @@
                 provider_segmentation_id=12345)
         cls.subnet2 = cls.create_subnet(cls.network2)
 
+    def _verify_dns_assignment(self, port):
+        expected_fqdn = '%s.%s' % (port['dns_name'], self.zone['name'])
+        self.assertEqual(expected_fqdn, port['dns_assignment'][0]['fqdn'])
+
     @decorators.idempotent_id('fa6477ce-a12b-41da-b671-5a3bbdafab07')
     def test_port_on_special_network(self):
         name = data_utils.rand_name('port-test')
         port = self.create_port(self.network2,
                                 dns_name=name)
+        self._verify_dns_assignment(port)
         addr = port['fixed_ips'][0]['ip_address']
         self._verify_dns_records(addr, name)
         self.client.delete_port(port['id'])