code: def testConstructor(self):
      comm = MPI.Comm()
      self.assertEqual(comm, MPI.COMM_NULL)
      self.assertIsNot(comm, MPI.COMM_NULL)
  
      def construct():
          MPI.Comm((1, 2, 3))
  
      self.assertRaises(TypeError, construct)
  
imports: from mpi4py import MPI
  import mpiunittest
label_desc: Use image node_id 1 for calling the TestCommNull obj's underlying member method code with example usage: obj.testConstructor() without return types