def prepend_lines(prepend, iterable):
    """Prepend every line in iterable with ``str``, most probably
    ``CHECK``.

    :param prepend:     ``str`` to prepend to every line in iterable.
    :param iterable:    Iterable to prepend with ``str``.
    :return:            Constructed ``str``.
    """
    return "\n".join([f"{prepend} {i}" for i in iterable])