code: def testStruct5(self):
      for t1, t2 in itertools.product(*[typecodes] * 2):
          with self.subTest(t1=t1, t2=t2):
              dtlist = []
              dt = np_dtype(f"c,{t1},{t2},c", align=True)
              dtlist.append(dt)
              for _ in range(3):
                  dt = np_dtype([("", dt)] * 2, align=True)
                  dtlist.append(dt)
              for dt in dtlist:
                  mt = fromnumpy(dt)
                  dt2 = tonumpy(mt)
                  mt.Free()
                  self.assertEqual(dt, dt2)
  
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 10 for calling the TestUtilDTLib obj's underlying member method code with example usage: obj.testStruct5() without return types