Abstract

Humans have been telling computers what to do for sixty years or more, and our methods have improved from setting switches on a panel to near-English computing languages and even graphical programming systems. Yet with frightening frequency, our instructions do not cause the behaviour we want, with consequences ranging from the annoying (the blue screen of death appearing on an airport schedule screen) to the tragic (a medical device overdosing a patient with radiation because of a threading error). Most programmers learn to live with the fear that comes from wondering whether the class, or the method, or even the line they have just written will do what they expect when executed.

In recent years software engineers have developed methods and tools that dramatically reduce the mismatch between programmer intention and machine behaviour. I will discuss a number of these tools, including Checkstyle, FindBugs, Jumble, Selenium, and JUnit, all of which my colleagues and I use daily. As a demonstration, I will undertake to make bug-free modifications to a program using specifications suggested by the audience, employing a coding style called “test-driven development”. To add spice, the program being modified will be the one that I am using to drive the presentation!