code: def testUnionMethod(self):
      g = Graph.Tree(7, 2).union(Graph.Lattice([7]))
      self.assertTrue(g.vcount() == 7 and g.ecount() == 12)
  
imports: import unittest
  from igraph import Graph, disjoint_union, intersection, union
label_desc: Use image node_id 10 for calling the OperatorTests obj's underlying member method code with example usage: obj.testUnionMethod() without return types