Lasse Koskela - Effective Unit Testing: A guide for Java Developers

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Few sights are as captivating as the pure joy of learning new things.

On the night of June 10, 2009, I found an email in my inbox from Christina Rudloff from Manning, asking me if I knew anyone who might be a good candidate to write a Java edition of Roy Osheroves book, The Art of Unit Testing in .NET. I told her Id do it.

That was a long time ago and what youre looking at right now has very little in common with Roys book. Let me explain.

The project started as a straight translation from .NET to Java, only rewriting where necessary to match the changing technology platform, its tooling, and its audience. I finished the first chapter, the second chapter, the third chapter, and suddenly I found myself rewriting not just short passages but entire chapters. The tone of voice wasnt mine; sometimes I would disagree or have preferences incompatible with Roys, and sometimes I simply felt strongly about saying something, setting things straight, and putting a stake into the ground.

Eventually, I decided to start over.

It was clear that we were not in a translation project. This was a brand new title of its owna book that helps a Java programmer improve his tests, gaining a deeper insight into what makes a test good and what kind of pitfalls to look out for. You can still see Roys thinking in many ways in this book. For instance, the chapter titles of the catalog in was written largely thanks to Roys counterpart in The Art of Unit Testing in .NET.

This is a book for the Java programmer. Yet, I didnt want to straitjacket the ideas in this book artificially, so I tried to steer away from being too language-specific even though all of the code examples in the pattern catalog, for example, are Java. Writing good tests is a language-agnostic problem and I heartily recommend you read this book thoughtfully, even if you happen to spend most of your office hours hacking on another programming language.

Along those same lines, I didnt want to give you a tutorial on JUnit or my favorite mock object library. Aside from such technology being a constantly changing landscape and bound to become stale information within months of publication, I wanted to write the kind of book that I would want to read. I like focused books that dont force me to lug around dead weight about a testing framework I already know by heart or a mock object library I dont use. For these reasons, Ive tried to minimize the amount of technology-specific advice. There is some but I want you to know that Ive done my best to keep it to a minimumjust enough to have meaningful conversations about the underlying concepts that I find essential in writing, running, maintaining, and improving tests.

I tried to write the book I wouldve wanted to read. I hope you will enjoy it and, most importantly, integrate some of these ideas into your own practice.

When I signed up to write this book I thought itd be a short project. Everything was supposed to be straightforward with no wildcards in sight. I shouldve known better. My wishful thinking was shattered as weeks turned to months and months turned to years. Without the help of many, many people this book would definitely not be in your hands and most likely itd still be a work-in-progress.

From the moment this project was initiated in a casual email exchange with Manning Publications Christina Rudloff, a massive amount of help has poured in and all of it has been very much appreciatedand needed.

Id like to thank the team at Manning for their support and persistence. In no specific order, Michael Stephens, Elle Suzuki, Steven Hong, Nick Chase, Karen Tegtmeyer, Sebastian Stirling, Candace M. Gillhoolley, Maureen Spencer, Ozren Harlovic, Frank Pohlmann, Benjamin Berg, Elizabeth Martin, Dottie Marsico, Janet Vail, and Mary Piergies.

A special thanks goes to the fine individuals that served as domain experts or reviewers and contributed their time to put their specific experience and expertise to improving this book. Again, in no specific order, Id like to extend my most sincere gratitude to Jeremy Anderson, Christopher Bartling, Jedidja Bourgeois, Kevin Con-away, Roger Cornejo, Frank Crow, Chad Davis, Gordon Dickens, Martyn Fletcher, Paul Holser, Andy Kirsch, Antti Koivisto, Paul Kronquist, Teppo Kurki, Franco Lombardo, Saicharan Manga, Dave Nicolette, Gabor Paller, J. B. Rainsberger, Joonas Reynders, Adam Taft, Federico Tomassetti, Jacob Tomaw, Bas Vodde, Deepak Vohra, Rick Wagner, Doug Warren, James Warren, Robert Wenner, Michael Williams, and Scott Sauyet. Special thanks to Phil Hanna for his technical review of the manuscript just before it went into production.

And last, but definitely not least, Id like to thank my family for their continued support. I imagine it has at times felt like a never-ending endeavor to get this book to print. Thank you for understanding all of those late nights with a computer on my lap and for carrying me through the rough spots.

Developer testing has been increasing its mindshare significantly among Java developers over the past 10 years or so. Today, no computer science student graduates without having at least read about automated unit tests and their importance in software development. The idea is simpleto ensure that our code works and keeps workingbut the skill takes significant effort to learn.