code: def test_filename_template_to_regex_unknown_variables():
      with pytest.raises(
          ValueError, match="Regex still contains variables.+"
      ):
          naming._filename_template_to_regex("{XYZ}")
  
imports: import os
  from absl.testing import parameterized
  from etils import epath
  import pytest
  from tensorflow_datasets import testing
  from tensorflow_datasets.core import naming
  from tensorflow_datasets.core import splits
label_desc: Use image node_id 31 for calling a global function with example usage: test_filename_template_to_regex_unknown_variables() without return types