def test_withPotentialDataLoss(self):
        """
        If the full body of the L{IResponse} passed to L{client.readBody} is
        not definitely received, the L{Deferred} returned by L{client.readBody}
        fires with a L{Failure} wrapping L{client.PartialDownloadError} with
        the content that was received.
        """
        response = DummyResponse()
        d = client.readBody(response)
        response.protocol.dataReceived(b"first")
        response.protocol.dataReceived(b"second")
        response.protocol.connectionLost(Failure(PotentialDataLoss()))
        failure = self.failureResultOf(d)
        failure.trap(client.PartialDownloadError)
        self.assertEqual({
            "status": failure.value.status,
            "message": failure.value.message,
            "body": failure.value.response,
        }, {
            "status": b"200",
            "message": b"OK",
            "body": b"firstsecond",
        })

        If the full body of the L{IResponse} passed to L{client.readBody} is
        not definitely received, the L{Deferred} returned by L{client.readBody}
        fires with a L{Failure} wrapping L{client.PartialDownloadError} with
        the content that was received.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_agent.py