code: def test_notify_payload(self):
      if self.conn.info.server_version < 90000:
          return self.skipTest(
              "server version %s doesn't support notify payload"
              % self.conn.info.server_version
          )
      self.autocommit(self.conn)
      self.listen("foo")
      pid = int(
          self.notify("foo", payload="Hello, world!").communicate()[0]
      )
      time.sleep(0.5)
      self.conn.poll()
      self.assertEqual(1, len(self.conn.notifies))
      notify = self.conn.notifies[0]
      self.assertEqual(pid, notify.pid)
      self.assertEqual("foo", notify.channel)
      self.assertEqual("Hello, world!", notify.payload)
  
imports: import unittest
  from collections import deque
  import psycopg2
  from psycopg2 import extensions
  from psycopg2.extensions import Notify
  from .testutils import ConnectingTestCase, skip_if_crdb, slow
  from .testconfig import dsn
  import sys
  import time
  import select
  from subprocess import Popen, PIPE
label_desc: Use image node_id 9 for calling the NotifiesTests obj's underlying member method code with example usage: obj.test_notify_payload() and returns: self