docs: def trigger_function_installed(connection: connection):
      """Test whether or not the psycopg2-pgevents trigger function is installed.
  
      Parameters
      ----------
      connection: psycopg2.extensions.connection
          Active connection to a PostGreSQL database.
  
      Returns
      -------
      bool
          True if the trigger function is installed, otherwise False.
  
      """
      installed = False
  
      log('Checking if trigger function installed...', logger_name=_LOGGER_NAME)
  
      try:
          execute(connection, "SELECT pg_get_functiondef('public.psycopg2_pgevents_create_event'::regproc);")
          installed = True
      except ProgrammingError as e:
          if e.args:
              error_stdout = e.args[0].splitlines()
              error = error_stdout.pop(0)
              if error.endswith('does not exist'):
                  # Trigger function not installed
                  pass
              else:
                  # Some other exception; re-raise
                  raise e
          else:
              # Some other exception; re-raise
              raise e
  
      log('...{}installed'.format('' if installed else 'NOT '), logger_name=_LOGGER_NAME)
  
      return installed