code: def test_invalid_format(es):
      output_path = "test1.xzy"
  
      with pytest.raises(ValueError) as excinfo:
          es.plot(to_file=output_path)
  
      assert str(excinfo.value).startswith("Unknown format")
  
file_path: featuretools/featuretools/tests/entityset_tests/test_plotting.py
imports: import os
  import re
  import graphviz
  import pandas
  import pytest
  from featuretools import EntitySet
  from featuretools.utils.gen_utils import Library
label_desc: Use image node_id 8 for calling a global function with example usage: test_invalid_format(es) without return types