code: def test_digraph(self):
      with pytest.raises(nx.NetworkXNotImplemented):
          G = nx.DiGraph()
          G.add_edge(0, 1)
          G.add_edge(1, 2)
          G.add_edge(2, 3)
          label_name = "label"
          G.nodes[0][label_name] = "A"
          G.nodes[3][label_name] = "B"
          node_classification.harmonic_function(G)
  
file_path: networkx/networkx/algorithms/tests/test_node_classification.py
imports: import pytest
  import networkx
  from networkx.algorithms import node_classification
label_desc: Use image node_id 5 for calling the TestLocalAndGlobalConsistency obj's underlying member method code with example usage: obj.test_digraph() without return types