def METHOD_NAME(test_obj):
    """
    produce the expected error message
    :param test_obj: NumaTest object
    :return: str, error message to be checked
    """
    hugepage_size = test_obj.params.get('hp_size')
    err_msg = ""
    if hugepage_size == 'scarce_mem':
        err_msg = "unable to map backing store for guest RAM: Cannot allocate memory"
    return err_msg