def METHOD_NAME(self):
    self._test_posting_duplicate_source_system_username(self.sources_url, self.rest_client)
    self.assertEqual(SourceSystem.objects.count(), 2)
    self.assertEqual(User.objects.count(), 3)
    source1_duplicate_username = SourceSystem.objects.get(name=self.source1_duplicate_username_dict["name"])
    self.assertEqual(source1_duplicate_username.name, self.source1_duplicate_username_dict["name"])
    self.assertEqual(source1_duplicate_username.type.pk, self.source1_duplicate_username_dict["type"])
    duplicate_username = self.source1_duplicate_username_dict["username"]
    generated_username = source1_duplicate_username.user.username
    self.assertNotEqual(generated_username, duplicate_username)
    self.assertTrue(generated_username.startswith(duplicate_username))