code: def testStruct4(self):
      for t in typecodes:
          with self.subTest(typecode=t):
              dt0 = np_dtype(t)
              mt0 = fromnumpy(dt0)
              stp, mt1 = self.makeStruct(t, mt0)
              ex1 = stp.itemsize
              for n, mt in (
                  (1, mt1),
                  (1, mt1.Dup()),
                  (1, mt1.Create_resized(0, 1 * ex1)),
                  (3, mt1.Create_resized(0, 3 * ex1)),
                  (3, mt1.Create_contiguous(3)),
                  (5, mt1.Create_subarray([5], [5], [0])),
                  (7, MPI.Datatype.Create_struct([7], [0], [mt1])),
              ):
                  dt = tonumpy(mt)
                  self.assertEqual(mt.extent, n * ex1)
                  self.assertEqual(dt.itemsize, n * ex1)
                  self.assertTrue(dt.isalignedstruct)
                  self.check(mt)
                  self.check(dt)
                  if mt != mt1:
                      mt.Free()
              mt0.Free()
              mt1.Free()
  
imports: from mpi4py import MPI
  from mpi4py.util.dtlib import from_numpy_dtype
  from mpi4py.util.dtlib import to_numpy_dtype
  import sys, os
  import itertools
label_desc: Use image node_id 9 for calling the TestUtilDTLib obj's underlying member method code with example usage: obj.testStruct4() without return types