def test_saveKeyEmptyPassphrase(self):
        """
        L{_saveKey} will choose an empty string for the passphrase if
        no-passphrase is C{True}.
        """
        base = FilePath(self.mktemp())
        base.makedirs()
        filename = base.child('id_rsa').path
        key = Key.fromString(privateRSA_openssh)
        _saveKey(key, {'filename': filename, 'no-passphrase': True,
            'format': 'md5-hex'})
        self.assertEqual(
            key.fromString(
                base.child('id_rsa').getContent(), None, b''),
            key)

        L{_saveKey} will choose an empty string for the passphrase if
        no-passphrase is C{True}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_ckeygen.py