new_contents: #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  from oslo_versionedobjects.tests import test_fields
  
  from zun.objects import fields
  
  
  class TestContainerStatus(test_fields.TestField):
      def setUp(self):
          super(TestContainerStatus, self).setUp()
          self.field = fields.ContainerStatus()
          self.coerce_good_values = [
              ('Error', 'Error'),
              ('Running', 'Running'),
              ('Stopped', 'Stopped'),
              ('Paused', 'Paused'),
              ('Unknown', 'Unknown'),
              ('Creating', 'Creating'),
          ]
          self.coerce_bad_values = ['bad_value']
          self.to_primitive_values = self.coerce_good_values[0:1]
          self.from_primitive_values = self.coerce_good_values[0:1]
  
      def test_stringify(self):
          self.assertEqual("'Error'",
                           self.field.stringify('Error'))
  
      def test_stringify_invalid(self):
          self.assertRaises(ValueError, self.field.stringify, 'bad_value')
  
  
  class TestTaskState(test_fields.TestField):
      def setUp(self):
          super(TestTaskState, self).setUp()
          self.field = fields.TaskState()
          self.coerce_good_values = [
              ('image_pulling', 'image_pulling'),
              ('container_creating', 'container_creating'),
              ('sandbox_creating', 'sandbox_creating'),
          ]
          self.coerce_bad_values = ['bad_value']
          self.to_primitive_values = self.coerce_good_values[0:1]
          self.from_primitive_values = self.coerce_good_values[0:1]
  
      def test_stringify(self):
          self.assertEqual("'image_pulling'",
                           self.field.stringify('image_pulling'))
  
      def test_stringify_invalid(self):
          self.assertRaises(ValueError, self.field.stringify, 'bad_value')
  
subject: Add tests for custom object fields