test.py

    def test_client_sends_body(self):
        d = self.cl.post_json(
            "testserv:8008", "foo/bar", timeout=10000,
            data={"a": "b"},
        )

        self.pump()

        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        client = clients[0][2].buildProtocol(None)

        # XXX is there a way to do this without a pair of intermediary StringTransports?
        client_transport = proto_helpers.StringTransport()
        client.makeConnection(client_transport)
        client_transport.producer.resumeProducing()

        server_transport = proto_helpers.StringTransport()
        server = HTTPChannel()
        server.makeConnection(server_transport)
        server.dataReceived(client_transport.value())

        self.assertEqual(len(server.requests), 1)
        request = server.requests[0]
        content = request.content.read()
        self.assertEqual(content, '{"a":"b"}')