def test_emptyLiteral(self):
        """
        The literal returns an empty L{bytes} instance
        when given an empty L{bytes} instance.
        """
        literal = self.literalFactory(0, self.deferred)
        data = b"leftover"

        leftover = literal.write(data)

        self.assertEqual(leftover, data)

        The literal returns an empty L{bytes} instance
        when given an empty L{bytes} instance.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_imap.py