def bool_to_tuple(input):
    """Converts a single :class:`bool <python:bool>` value to a
    :class:`tuple <python:tuple>` of form ``(bool, bool)``.

    :param input: Value that should be converted.
    :type input: :class:`bool <python:bool>` / 2-member :class:`tuple <python:tuple>`

    :returns: :class:`tuple <python:tuple>` of form (:class:`bool <python:bool>`,
      :class:`bool <python:bool>`)
    :rtype: :class:`tuple <python:tuple>`

    :raises ValueError: if ``input`` is not a :class:`bool <python:bool>` or
      2-member :class:`tuple <python:tuple>`
    """
    if input is True:
        input = True, True
    elif not input:
        input = False, False
    elif not isinstance(input, tuple) or len(input) > 2:
        raise ValueError('input was neither a bool nor a 2-member tuple')
    return input
