def test_requestAvatarIdWithoutSignature(self):
        """
        L{SSHPublicKeyDatabase.requestAvatarId} should raise L{ValidPublicKey}
        if the credentials represent a valid key without a signature.  This
        tells the user that the key is valid for login, but does not actually
        allow that user to do so without a signature.
        """
        def _checkKey(ignored):
            return True
        self.patch(self.checker, 'checkKey', _checkKey)
        credentials = SSHPrivateKey(
            b'test', b'ssh-rsa', keydata.publicRSA_openssh, None, None)
        d = self.checker.requestAvatarId(credentials)
        return self.assertFailure(d, ValidPublicKey)

        L{SSHPublicKeyDatabase.requestAvatarId} should raise L{ValidPublicKey}
        if the credentials represent a valid key without a signature.  This
        tells the user that the key is valid for login, but does not actually
        allow that user to do so without a signature.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_checkers.py