code: def testLegacyAck(self):
      comm = self.COMM
      with warnings.catch_warnings():
          warnings.simplefilter("ignore", category=DeprecationWarning)
          comm._Failure_ack()
  
imports: from mpi4py import MPI
  import mpiunittest
  import warnings
  import struct
label_desc: Use image node_id 11 for calling the BaseTestULFM obj's underlying member method code with example usage: obj.testLegacyAck() without return types