def assert_bool(**kwargs):
    """Ensure all given values are boolean.

    :raises TypeError: if value is not ``True`` or ``False.

    .. versionadded:: 0.5.4
    """
    for label, subject in kwargs.items():
        if not isinstance(subject, bool):
            fmt = '{0} must be a bool, not {1}'
            msg = fmt.format(label, repr(subject))
            raise TypeError(msg)
