code: def test_saving_png_file(simple_feat, tmp_path):
      output_path = str(tmp_path.joinpath("test1.png"))
      graph_feature(simple_feat, to_file=output_path)
      assert os.path.isfile(output_path)
  
imports: import json
  import os
  import re
  import graphviz
  import pytest
  from featuretools.feature_base import AggregationFeature, DirectFeature, FeatureOutputSlice, GroupByTransformFeature, IdentityFeature, TransformFeature, graph_feature
  from featuretools.primitives import Count, CumMax, Mode, NMostCommon, Year
label_desc: Use image node_id 4 for calling a global function with example usage: test_saving_png_file(simple_feat, tmp_path) without return types