def test_unprintableCharacters(self):
        """
        When L{HistoricRecvLine} receives a keystroke for an unprintable
        function key with no assigned behavior, the line buffer is unmodified.
        """
        kR = lambda ch: self.p.keystrokeReceived(ch, None)
        pt = self.pt

        for ch in (pt.F1, pt.F2, pt.F3, pt.F4, pt.F5, pt.F6, pt.F7, pt.F8,
                   pt.F9, pt.F10, pt.F11, pt.F12, pt.PGUP, pt.PGDN):
            kR(ch)
            self.assertEqual(self.p.currentLineBuffer(), (b'', b''))

        When L{HistoricRecvLine} receives a keystroke for an unprintable
        function key with no assigned behavior, the line buffer is unmodified.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_recvline.py