code: def test_reciprocity_graph_isolated_nodes(self):
      with pytest.raises(nx.NetworkXError):
          DG = nx.DiGraph([(1, 2)])
          DG.add_node(4)
          nx.reciprocity(DG, 4)
  
file_path: networkx/networkx/algorithms/tests/test_reciprocity.py
imports: import pytest
  import networkx
label_desc: Use image node_id 5 for calling the TestReciprocity obj's underlying member method code with example usage: obj.test_reciprocity_graph_isolated_nodes() without return types