Unit Testing Simple Request-Response Protocols

Many of the XMPP protocols are simple: one side sends an IQ request, the other side receives the request, processes it, and responds with an IQ result. An example of such a simple request-response protocol is the software version protocol illustrated earlier. An implementation of this protocol consists of two parts:

  • The initiator implementation sends a software version request and processes the corresponding response when it comes in.

  • The responder listens for incoming software version requests and responds to them.

These implementations are typically implemented locally in one class for the initiator and one for the responder.[15] Example 7-1 shows how a VersionResponder class is instantiated in a client to respond to incoming software version requests. All this class does is listen for an incoming IQ query of the type jabber:iq:version, and respond with the values set through setVersion. The class uses the central XMPPClient class to send data to and receive data from the XMPP connection.

Example 7-1. Using VersionResponder to listen and respond to software version requests

class MyClient {
  MyClient() {
    xmppClient = new XMPPClient("alice@wonderland.lit", "mypass");
    versionResponder = new VersionResponder(xmppClient);
    versionResponder->setVersion("Swift", "0.1");
    xmppClient->connect();
  }
  …
};

Since the implementation of request-response protocols is local to one class, unit testing is a good way to test the functionality of the protocol ...

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