def test_saveKeyBadFingerPrintformat(self):
        """
        L{_saveKey} raises C{keys.BadFingerprintFormat} when unsupported
        formats are requested.
        """
        base = FilePath(self.mktemp())
        base.makedirs()
        filename = base.child('id_rsa').path
        key = Key.fromString(privateRSA_openssh)
        with self.assertRaises(BadFingerPrintFormat) as em:
            _saveKey(key, {'filename': filename, 'pass': 'passphrase',
                'format': 'sha-base64'})
        self.assertEqual('Unsupported fingerprint format: sha-base64',
            em.exception.args[0])

        L{_saveKey} raises C{keys.BadFingerprintFormat} when unsupported
        formats are requested.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_ckeygen.py