code: def test_returns_digraph_object(simple_feat):
      graph = graph_feature(simple_feat)
      assert isinstance(graph, graphviz.Digraph)
  
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 3 for calling a global function with example usage: test_returns_digraph_object(simple_feat) without return types