@classmethod
def _test_scheme_salt(cls, scheme):
    """
            Test if the scheme need a salt or raise BadScheme

            :param bytes scheme: A scheme
            :raises BadScheme: if ``scheme` require no salt
        """
    if scheme not in cls.schemes_salt:
        cls._raise_bad_scheme(scheme, cls.schemes_salt,
            'The scheme %r is only valid without a salt. Valide schemes with salt are %s.'
            )
