def METHOD_NAME(self):
    """
    produce the expected error message
    :return: str, error message to be checked
    """
    err_msg = self.params.get('err_msg', '')
    mem_mode = self.params.get('mem_mode')
    single_host_node = self.params.get('single_host_node')
    if not libvirt_version.version_compare(9, 3, 0) and \
            mem_mode == 'preferred' and \
            single_host_node is not None and \
            single_host_node != 'yes':
        new_err_msg = "NUMA memory tuning in 'preferred' mode only supports single node"
        err_msg = "%s|%s" % (err_msg, new_err_msg) if err_msg else new_err_msg
    return err_msg