code: def test_var_names_key_error(data):
      with pytest.raises(KeyError, match="bad_var_name"):
          _var_names(("theta", "tau", "bad_var_name"), data)
  
imports: from unittest.mock import Mock
  import numpy
  import pytest
  import scipy.stats
  from ...data import dict_to_dataset, from_dict, load_arviz_data
  from ...stats.density_utils import _circular_mean, _normalize_angle, _find_hdi_contours
  from ...utils import _stack, _subset_list, _var_names, expand_dims, flatten_inference_data_to_dict, one_de, two_de
  from ..helpers import TestRandomVariable
label_desc: Use image node_id 5 for calling a global function with example usage: test_var_names_key_error(data) without return types