code: def test_sendfile_force_unsupported_native(self):
      if sys.platform == "win32":
          if isinstance(self.loop, asyncio.ProactorEventLoop):
              self.skipTest("Fails on proactor event loop")
      srv_proto, cli_proto = self.prepare_sendfile()
  
      def sendfile_native(transp, file, offset, count):
          # to raise SendfileNotAvailableError
          return base_events.BaseEventLoop._sendfile_native(
              self.loop, transp, file, offset, count
          )
  
      self.loop._sendfile_native = sendfile_native
  
      with self.assertRaisesRegex(
          asyncio.SendfileNotAvailableError, "not supported"
      ):
          self.run_loop(
              self.loop.sendfile(
                  cli_proto.transport, self.file, fallback=False
              )
          )
  
      cli_proto.transport.close()
      self.run_loop(srv_proto.done)
      self.assertEqual(srv_proto.nbytes, 0)
      self.assertEqual(self.file.tell(), 0)
  
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 5 for calling the SendfileMixin obj's underlying member method code with example usage: obj.test_sendfile_force_unsupported_native() and returns: base_events