code: def test_sendfile_pre_and_post_data(self):
      srv_proto, cli_proto = self.prepare_sendfile()
      PREFIX = b"PREFIX__" * 1024  # 8 KiB
      SUFFIX = b"--SUFFIX" * 1024  # 8 KiB
      cli_proto.transport.write(PREFIX)
      ret = self.run_loop(
          self.loop.sendfile(cli_proto.transport, self.file)
      )
      cli_proto.transport.write(SUFFIX)
      cli_proto.transport.close()
      self.run_loop(srv_proto.done)
      self.assertEqual(ret, len(self.DATA))
      self.assertEqual(srv_proto.data, PREFIX + self.DATA + SUFFIX)
      self.assertEqual(self.file.tell(), len(self.DATA))
  
imports: import asyncio
  import errno
  import os
  import socket
  import sys
  import tempfile
  import unittest
  from asyncio import base_events
  from asyncio import constants
  from unittest import mock
  from test import support
  from test.support import os_helper
  from test.support import socket_helper
  from test.test_asyncio import utils
label_desc: Use image node_id 8 for calling the SendfileMixin obj's underlying member method code with example usage: obj.test_sendfile_pre_and_post_data() without return types