def METHOD_NAME(self):
    self.assertEqual(
        'country',
        extract_instance_id_from_nodeset_ref("instance('country')/country_list/country"),
    )
    self.assertEqual(
        'first',
        extract_instance_id_from_nodeset_ref("instance('first')/instance('second')country_list/country"),
    )
    self.assertEqual(
        None,
        extract_instance_id_from_nodeset_ref("foo('country')/country_list/country"),
    )
    self.assertEqual(
        None,
        extract_instance_id_from_nodeset_ref("foo/country_list/country"),
    )
    self.assertEqual(
        None,
        extract_instance_id_from_nodeset_ref(""),
    )
    self.assertEqual(
        None,
        extract_instance_id_from_nodeset_ref(None),
    )