code: def test_discover_master_error(sentinel):
      with pytest.raises(MasterNotFoundError):
          sentinel.discover_master("xxx")
  
imports: import socket
  from unittest import mock
  import pytest
  import redis.sentinel
  from redis import exceptions
  from redis.sentinel import MasterNotFoundError, Sentinel, SentinelConnectionPool, SlaveNotFoundError
label_desc: Use image node_id 5 for calling a global function with example usage: test_discover_master_error(sentinel) without return types