def test_setFrom(self):
        """
        When a message has no I{From:} header, a I{From:} value can be
        specified with the I{-F} flag.
        """
        stdin = NativeStringIO(
            'To: invaliduser2@example.com\n'
            'Subject: A wise guy?\n\n')
        self.patch(sys, 'stdin', stdin)
        o = parseOptions(["-F", "Larry <invaliduser1@example.com>", "-t"])
        self.assertEqual(o.sender, "Larry <invaliduser1@example.com>")

        When a message has no I{From:} header, a I{From:} value can be
        specified with the I{-F} flag.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_mailmail.py