new_contents: import datetime
  import unittest
  
  import solution
  
  
  class TestSocialGraph(unittest.TestCase):
      def setUp(self):
          self.terry = solution.User("Terry Gilliam")
          self.eric = solution.User("Eric Idle")
          self.graham = solution.User("Graham Chapman")
          self.john = solution.User("John Cleese")
          self.michael = solution.User("Michael Palin")
          self.graph = solution.SocialGraph()
          self.graph.add_user(self.terry)
          self.graph.add_user(self.eric)
          self.graph.add_user(self.graham)
          self.graph.add_user(self.john)
          self.graph.add_user(self.michael)
  
      def test_add_get_and_delete_user(self):
          with self.assertRaises(solution.UserAlreadyExistsError):
              self.graph.add_user(self.terry)
          self.graph.delete_user(self.terry.uuid)
          self.graph.add_user(self.terry)
          self.assertEqual(self.graph.get_user(self.terry.uuid), self.terry)
  
      def test_following(self):
          self.graph.follow(self.terry.uuid, self.eric.uuid)
          self.assertTrue(
              self.graph.is_following(self.terry.uuid, self.eric.uuid))
          self.assertFalse(
              self.graph.is_following(self.eric.uuid, self.terry.uuid))
  
      def test_friends(self):
          self.graph.follow(self.terry.uuid, self.eric.uuid)
          self.assertNotIn(self.eric.uuid, self.graph.friends(self.terry.uuid))
          self.assertNotIn(self.terry.uuid, self.graph.friends(self.eric.uuid))
          self.graph.follow(self.eric.uuid, self.terry.uuid)
          self.assertIn(self.eric.uuid, self.graph.friends(self.terry.uuid))
          self.assertIn(self.terry.uuid, self.graph.friends(self.eric.uuid))
  
  
  class TestUser(unittest.TestCase):
      def setUp(self):
          self.michael = solution.User("Michael Palin")
  
      def test_has_uuid(self):
          self.assertIsNotNone(getattr(self.michael, 'uuid'))
  
      def test_add_post(self):
          self.michael.add_post("larodi")
          post = next(self.michael.get_post())
          self.assertEqual(post.author, self.michael.uuid)
          self.assertEqual(post.content, "larodi")
          self.assertTrue(isinstance(post.published_at, datetime.datetime))
  
  if __name__ == '__main__':
      unittest.main()
  
subject: Add 03-task sample test file.