FrazzledDad writes "'We let the tests we wrote do more harm than good.' That snippet from the preface of Roy Osherove's The Art of Unit Testing with Examples in .NET (AOUT hereafter) is the wrap up of a frank description of a failed project Osherove was part of. The goal of AOUT is teaching you great approaches to unit testing so you won't run into similar failures on your own projects." Keep reading for the rest of FrazzledDad's review.AOUT is a well-written, concise book walking readers through many different aspects of unit testing. Osherove's book has something for all readers, regardless of their experience with unit testing. While the book's primary focus is .NET, the concepts apply to many different platforms, and Osherove also covers a few Java tools as well.
Osherove has a long history of advocating testing in the .NET space. He's blogged about it extensively, speaks at many international conferences, and leads a large number of Agile and testing classes. He's also the chief architect at TypeMock, an isolation framework that's a tool you may make use of in your testing efforts – and he's very up front about his involvement with that tool when discussing isolation techniques in the book. He does a very good job of not pushing his specific tool and also covers several others, leaving me feeling there wasn't any bias toward his product whatsoever.
AOUT does a number of different things really, really well. First off, it focuses solely on unit testing. Early on Osherove lays out the differences between unit and integration tests, but he quickly moves past that and stays with unit tests the rest of the book. Secondly, Osherove avoids pushing any particular methodology (Test Driven Development, Behavior Driven Development, etc.) and just stays on critical concepts around unit testing.
I particularly appreciated that latter point. While I'm a proponent of *DD, it was nice to read through the book without having to filter out any particular dogma biases. I think that mindset makes this book much more approachable and useful to a broader audience – dive in to unit testing and learn the fundamentals before moving on to the next step.
I also enjoyed that Osherove carries one example project through the entire book. He takes readers through a journey as he builds a log analyzer and uses that application to drive discussion of specific testing techniques. There are other examples used in the book, but they're all specific to certain situations; the brunt of his discussion remains on the one project which helps keep readers focused in the concepts Osherove's laying out.
The book's first two chapters are the obligatory introduction to unit testing frameworks and concepts. Osherove quickly moves through discussions of "good" unit tests, offers up a few paragraphs on TDD, and lays out a few bits around unit test frameworks in general. After that he's straight in to his "Core Techniques" section where he discusses stubs, mocks, and isolation frameworks. The third part, "The Test Code" covers hierarchies and pillars of good testing. The book finishes with "Design and Process" which hits on getting testing solidly integrated into your organization, plus has a great section on trying to deal with testing legacy systems. There are a couple handy appendices covering design issues and tooling.
Osherove uses his "Core Techniques" section to clearly lay out the differences between stubs and mocks, plus he covers using isolation frameworks such as Rhino.Mocks or TypeMock to assist with implementing these concepts. I enjoyed reading this section because too many folks confuse the concepts of stubbing and mocking. They're not interchangeable, and Osherove does a great job emphasizing where you should use stubs and mocks to deal with dependencies and interactions, respectively.
The walkthrough of splitting out a dependency and using a stub is a perfect example of why this book's so valuable: Osherove clearly steps through pulling the dependency out to an interface, then shows you different methods of using a stub for testing via injection by constructors, properties, or method parameters. He's also very clear about the drawbacks of each approach, something I find critical in any design-related discussion – let me know what things might cause me grief later on!
While the discussion on mocking, stubbing, and isolation was informative and well-written, I got the most out of chapters 6 ("Test hierarchies and organization") and 7 ("The pillars of good tests"). The hierarchy discussion in particular caused me to re-think how I've been organizing an evolving suite of Selenium-based UI tests. I was already making use of DRY and refactoring out common functionality into factory and helper methods; however, Osherove's discussion led to me re-evaluating the overall structure, resulting in some careful use of base class and inheritance. His concrete examples of building out a usable test API for your environment also changed how I was handling namespaces and general naming.
If you're in an organization that's new to testing, or if you're trying to deal with getting testing around legacy software, then the last two chapters of the book are must-read sections. Changing cultures inside organizations is never easy, and Osherove shows a number of different tools you can use when trying to drive the adoption of testing in your organizations. My own experience has shown you'll need to use combinations of many of these including finding champions, getting management buy off, and most importantly learning how to deal with the folks who become roadblocks.
The Art of Unit Testing does a lot of things really well. I didn't feel the book did anything poorly, and I happily include it in my list of top software engineering/craftsmanship books I've read. All software developers, regardless of their experience with unit testing, stand to learn something from it.
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