code: def test_key_error(self):
      with self.assertRaises(KeyError):
          self.flags["unknown key"]
  
file_path: cupy/tests/cupy_tests/core_tests/test_flags.py
imports: import unittest
  from cupy._core import flags
  from cupy import testing
label_desc: Use image node_id 5 for calling the TestFlags obj's underlying member method code with example usage: obj.test_key_error() without return types