code: def fail():
      raise ValueError("Expected failure.")
  
imports: from __future__ import annotations
  from datetime import datetime, timedelta
  from airflow.models.dag import DAG
  from airflow.operators.empty import EmptyOperator
  from airflow.operators.python import PythonOperator
  from airflow.utils.trigger_rule import TriggerRule
label_desc: Use image node_id 1 for calling a global function with example usage: fail() without return types