def METHOD_NAME(self, input_data=None):
  """Mock subprocess.Popen.communicate."""
  if '/fake/build_dir/fake_fuzzer' in self.command:
    if '-merge=1' in self.command:
      # Mock merge.
      self._do_merge()
    else:
      # Mock writing of new units.
      self._write_fake_units()
  if self.stdout:
    self.stdout.write(output)
  return None, None