def test_signDataRSAErrbackOnUnknownBlob(self):
        """
        Assert that we get an errback if we try to sign data using a key that
        wasn't added.
        """
        del self.server.factory.keys[self.rsaPublic.blob()]
        d = self.client.signData(self.rsaPublic.blob(), b"John Hancock")
        self.pump.flush()
        return self.assertFailure(d, ConchError)

        Assert that we get an errback if we try to sign data using a key that
        wasn't added.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_agent.py