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When testing UI controls, automated unit testing is usually not practical. Why? Because to verify if a UI control is working correctly, you generally have to look at the screen and see if it looks right. Looking at the screen often entails more than just checking that the various fields have the right data. Often there are interactions between the controls, focus issues, or painting artifacts that a human can detect more easily than a mindless unit-testing program. Don’t get me wrong: Automated unit testing with systems like NUnit and JUnit is definitely advisable for code that doesn’t have a user interface.

You can download SystemBrowser’s complete source code from the Source Code area of the Apress Web site (www.apress.com).

With this case study, you’ve seen how to use events and Coordinator teams to implement a multithreaded service component. I also showed you how to use events and Coordinator teams to create the supporting test programs. By developing HttpService as a component with no coupling to other components, HttpService is independently deployable. Moreover, because its worker classes are also completely decoupled from other classes, the workers are relatively simple to test and easy to reuse.

In this case study, I’ve shown a fairly small distributed system, whose individual components are all very simple. The complexity of the overall system—like most distributed systems—is due mainly to the interactions between the various parts. While class diagrams are useful to describe the design of individual components, wiring diagrams are generally more helpful in depicting the whole system.

Software development is one of those activities that just seems to be inherently complicated, so anything you can do to simplify the job is useful. Using events to avoid coupling between the key parts of a system is often a great way to simplify design, testing, and maintenance. My hope is that you finish reading this book feeling that event-based programming is not just a fad, but also a reasonable way to create software in today’s world of shrinking budgets, timelines, and product shelf lives. Go for it!