code: def test_digraph(self):
      G = nx.DiGraph()
      H = node_link_graph(node_link_data(G))
      assert H.is_directed()
  
file_path: networkx/networkx/readwrite/json_graph/tests/test_node_link.py
imports: import json
  import pytest
  import networkx
  from networkx.readwrite.json_graph import node_link_data, node_link_graph
label_desc: Use image node_id 5 for calling the TestNodeLink obj's underlying member method code with example usage: obj.test_digraph() without return types