'should warn on invalid separator'

def test_invalid_sep(self):

    msg = 'Unsafe    Signer    separator:    %r    (cannot    be    empty    or    consist    of    only    A-z0-9-_=)'
    separators = ['', '-', 'abc']
    for sep in separators:
        with self.assertRaisesMessage(ValueError, (msg % sep)):
            signing.Signer(sep=sep)
