'Test creating an orphan returns an error'

def test_move_child_creates_orphan_error(self):

    unit_1_key = self.response_usage_key(self.create_xblock(parent_usage_key=self.seq2_usage_key, category='vertical', display_name='unit    1'))
    unit_2_key = self.response_usage_key(self.create_xblock(parent_usage_key=self.seq2_usage_key, category='vertical', display_name='unit    2'))
    resp = self.client.ajax_post(self.seq2_update_url, data={'children': [unicode(unit_1_key)]})
    self.assertEqual(resp.status_code, 400)
    self.assertIn('Invalid    data,    possibly    caused    by    concurrent    authors', resp.content)
    self.assertListEqual(self.get_item_from_modulestore(self.seq2_usage_key).children, [unit_1_key, unit_2_key])
