def test_getCipher(self):
        """
        Test that the _getCipher method returns the correct cipher.
        """
        ciphers = transport.SSHCiphers(b'A', b'B', b'C', b'D')
        iv = key = b'\x00' * 16
        for cipName, (algClass, keySize, counter) in ciphers.cipherMap.items():
            cip = ciphers._getCipher(cipName, iv, key)
            if cipName == b'none':
                self.assertIsInstance(cip, transport._DummyCipher)
            else:
                self.assertIsInstance(cip.algorithm, algClass)

        Test that the _getCipher method returns the correct cipher.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_transport.py