def _check_utf8_encoding(self, bstring):
        """
        Check whether the given sequence of bytes
        is properly encoded in UTF-8.

        :param bytes bstring: the byte string to be checked
        """
        if not gf.is_bytes(bstring):
            self._failed(u"The given string is not a sequence of bytes")
            return
        if not gf.is_utf8_encoded(bstring):
            self._failed(u"The given string is not encoded in UTF-8.")
Check whether the given sequence of bytes
        is properly encoded in UTF-8.

        :param bytes bstring: the byte string to be checked