def es_index_successful(response):
    """
    Test if an Elasticsearch client ``index`` method response indicates a
    successful index operation. The response parameter should be a dictionary
    with following keys:

    .. sourcecode:: python

        {
            '_shards': {
                'total': 2,
                'failed': 0,
                'successful': 1
            },
            '_index': u'billing-2015-12',
            '_type': u'billing',
            '_id': u'AVOmKFXgF_o3S6_4PkP1',
            '_version': 1,
            'created': True
        }

    According to `Elasticsearch Index API <https://www.elastic.co/guide/en/
    elasticsearch/reference/current/docs-index_.html>`, an index operation is
    successful in the case ``successful`` is at least 1.

    :rtype: bool
    """
    return response.get('_shards', {}).get('successful', 0) >= 1