code: def test_domrel_png(self):
      # Graph taken from https://commons.wikipedia.org/wiki/File:Domrel.png
      edges = [(1, 2), (2, 3), (2, 4), (2, 6), (3, 5), (4, 5), (5, 2)]
      G = nx.DiGraph(edges)
      result = nx.immediate_dominators(G, 1)
      assert result == {1: 1, 2: 1, 3: 2, 4: 2, 5: 2, 6: 2}
      # Test postdominance.
      result = nx.immediate_dominators(G.reverse(copy=False), 6)
      assert result == {1: 2, 2: 6, 3: 5, 4: 5, 5: 2, 6: 6}
  
imports: import pytest
  import networkx
label_desc: Use image node_id 8 for calling the TestImmediateDominators obj's underlying member method code with example usage: obj.test_domrel_png() without return types