class_docstr: Unit testing for the cd index function.
code: def test_n_equals_zero(self):
      G = nx.DiGraph()
      G.add_nodes_from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
      G.add_edge(4, 2)
      G.add_edge(4, 0)
      G.add_edge(4, 3)
      G.add_edge(6, 4)
      G.add_edge(7, 4)
      G.add_edge(8, 4)
      G.add_edge(9, 4)
      G.add_edge(9, 1)
      G.add_edge(10, 4)
  
      node_attrs = {
          0: {"time": datetime(1992, 1, 1)},
          1: {"time": datetime(1992, 1, 1)},
          2: {"time": datetime(1993, 1, 1)},
          3: {"time": datetime(1993, 1, 1)},
          4: {"time": datetime(1995, 1, 1)},
          5: {"time": datetime(2005, 1, 1)},
          6: {"time": datetime(2010, 1, 1)},
          7: {"time": datetime(2001, 1, 1)},
          8: {"time": datetime(2020, 1, 1)},
          9: {"time": datetime(2017, 1, 1)},
          10: {"time": datetime(2004, 4, 1)},
      }
  
      nx.set_node_attributes(G, node_attrs)
  
      with pytest.raises(
          nx.NetworkXError, match="The cd index cannot be defined."
      ) as ve:
          nx.cd_index(G, 4, time_delta=_delta)
  
file_path: networkx/networkx/algorithms/tests/test_time_dependent.py
imports: from datetime import datetime, timedelta
  import pytest
  import networkx
label_desc: Use image node_id 8 for calling the TestCdIndex obj's underlying member method code with example usage: obj.test_n_equals_zero() without return types