code: def testGetTrueExtent(self):
      for dtype in datatypes:
          try:
              lb, ext = dtype.Get_true_extent()
              self.assertEqual(dtype.true_lb, lb)
              self.assertEqual(dtype.true_ub, lb + ext)
              self.assertEqual(dtype.true_extent, ext)
          except NotImplementedError:
              self.skipTest("mpi-type-get_true_extent")
  
imports: from mpi4py import MPI
  import mpiunittest
  import struct
label_desc: Use image node_id 4 for calling the TestDatatype obj's underlying member method code with example usage: obj.testGetTrueExtent() without return types