Used in https://github.com/mhenc/airflow/blob/master/airflow/dag_processing/manager.py#L613

should be straighforward
"""
        Simple utility method to set dependency between two tasks that
        already have been added to the DAG using add_task()
        """
        self.get_task(upstream_task_id).set_downstream(self.get_task(downstream_task_id))
    @provide_session
    def get_task_instances_before(