code: def testUnion(self):
      g = Graph.Tree(7, 2) | Graph.Lattice([7])
      self.assertTrue(g.vcount() == 7 and g.ecount() == 12)
      self.assertTrue(
          sorted(g.get_edgelist())
          == [
              (0, 1),
              (0, 2),
              (0, 6),
              (1, 2),
              (1, 3),
              (1, 4),
              (2, 3),
              (2, 5),
              (2, 6),
              (3, 4),
              (4, 5),
              (5, 6),
          ]
      )
  
imports: import unittest
  from igraph import Graph, disjoint_union, intersection, union
label_desc: Use image node_id 8 for calling the OperatorTests obj's underlying member method code with example usage: obj.testUnion() without return types