def test_ciphersAreValid(self):
        """
        Test that all the supportedCiphers are valid.
        """
        ciphers = transport.SSHCiphers(b'A', b'B', b'C', b'D')
        iv = key = b'\x00' * 16
        for cipName in self.proto.supportedCiphers:
            self.assertTrue(ciphers._getCipher(cipName, iv, key))

        Test that all the supportedCiphers are valid.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_transport.py