code: def test_relabel_nodes_function(self):
      G = nx.empty_graph()
      G.add_edges_from([("A", "B"), ("A", "C"), ("B", "C"), ("C", "D")])
      # function mapping no longer encouraged but works
  
      def mapping(n):
          return ord(n)
  
      H = nx.relabel_nodes(G, mapping)
      assert nodes_equal(H.nodes(), [65, 66, 67, 68])
  
imports: import pytest
  import networkx
  from networkx.generators.classic import empty_graph
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 5 for calling the TestRelabel obj's underlying member method code with example usage: obj.test_relabel_nodes_function() and returns: ord