code: def testIndexedBlock(self):
      for dtype in datatypes:
          for block in range(5):
              blocklengths = list(range(block, block + 5))
              displacements = [0]
              for b in blocklengths[:-1]:
                  stride = displacements[-1] + b * dtype.extent + 1
                  displacements.append(stride)
              factory = MPI.Datatype.Create_indexed_block
              args = (block, displacements)
              self.check(dtype, factory, *args)
  
imports: from mpi4py import MPI
  import mpiunittest
  import struct
label_desc: Use image node_id 9 for calling the BaseTestDatatypeCreateMixin obj's underlying member method code with example usage: obj.testIndexedBlock() without return types