'Ensure str(future) returns without error'

def test_string_coverage(self):

    cluster = Cluster(protocol_version=PROTOCOL_VERSION)
    session = cluster.connect()
    query = 'SELECT    *    FROM    system.local'
    statement = SimpleStatement(query)
    future = session.execute_async(statement)
    self.assertIn(query, str(future))
    future.result()
    self.assertIn(query, str(future))
    self.assertIn('result', str(future))
    cluster.shutdown()
