It has been said before but it bears repeating: Writing defect-free software is

exceedingly diffi cult. Proof of correctness of real systems is still well beyond our

abilities, and specifi cation of behavior is equally challenging. Predicting future

needs is a hit or miss affair—we’d all be getting rich on the stock market instead

of building software systems if we were any good at it!

Automated verifi cation of software behavior is one of the biggest advances in

development methods in the last few decades. This very developer-friendly practice

has huge benefi ts in terms of increasing productivity, improving quality, and

keeping software from becoming brittle. The very fact that so many developers

are now doing it of their own free will speaks for its effectiveness.

This chapter introduces the concept of test automation using a variety of

tools (including xUnit), describes why you would do it, and explains what

makes it diffi cult to do test automation well.