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Test Driven Development: By Example Paperback – Nov 8 2002
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From the Inside Flap
Clean code that works, in Ron Jeffries' pithy phrase, is the goal of Test-Driven Development (TDD). Clean code that works is a worthwhile goal for a whole bunch of reasons.
But how do we get to clean code that works? Many forces drive us away from clean code, and even from code that works. Without taking too much counsel of our fears, here's what we do: we drive development with automated tests, a style of development called Test-Driven Development (TDD). In Test-Driven Development, we
These are two simple rules, but they generate complex individual and group behavior with technical implications such as the following.
The two rules imply an order to the tasks of programming.
Red/green/refactor--the TDD mantra.
Assuming for the moment that such a programming style is possible, it further might be possible to dramatically reduce the defect density of code and make the subject of work crystal clear to all involved. If so, then writing only that code which is demanded by failing tests also has social implications.
So the concept is simple, but what's my motivation? Why would a software engineer take on the additional work of writing automated tests? Why would a software engineer work in tiny little steps when his or her mind is capable of great soaring swoops of design? Courage.Courage
Test-driven development is a way of managing fear during programming. I don't mean fear in a bad way--pow widdle prwogwammew needs a pacifiew-but fear in the legitimate, this-is-a-hard-problem-and-I-can't-see-the-end-from-the-beginning sense. If pain is nature's way of saying "Stop!" then fear is nature's way of saying "Be careful." Being careful is good, but fear has a host of other effects.
None of these effects are helpful when programming, especially when programming something hard. So the question becomes how we face a difficult situation and,
Imagine programming as turning a crank to pull a bucket of water from a well. When the bucket is small, a free-spinning crank is fine. When the bucket is big and full of water, you're going to get tired before the bucket is all the way up. You need a ratchet mechanism to enable you to rest between bouts of cranking. The heavier the bucket, the closer the teeth need to be on the ratchet.
The tests in test-driven development are the teeth of the ratchet. Once we get one test working, we know it is working, now and forever. We are one step closer to having everything working than we were when the test was broken. Now we get the next one working, and the next, and the next. By analogy, the tougher the programming problem, the less ground that each test should cover.
Readers of my book Extreme Programming Explained will notice a difference in tone between Extreme Programming (XP) and TDD. TDD isn't an absolute the way that XP is. XP says, "Here are things you must be able to do to be prepared to evolve further." TDD is a little fuzzier. TDD is an awareness of the gap between decision and feedback during programming, and techniques to control that gap. "What if I do a paper design for a week, then test-drive the code? Is that TDD?" Sure, it's TDD. You were aware of the gap between decision and feedback, and you controlled the gap deliberately.
That said, most people who learn TDD find that their programming practice changed for good. Test Infected is the phrase Erich Gamma coined to describe this shift. You might find yourself writing more tests earlier, and working in smaller steps than you ever dreamed would be sensible. On the other hand, some software engineers learn TDD and then revert to their earlier practices, reserving TDD for special occasions when ordinary programming isn't making progress.
There certainly are programming tasks that can't be driven solely by tests (or at least, not yet). Security software and concurrency, for example, are two topics where TDD is insufficient to mechanically demonstrate that the goals of the software have been met. Although it's true that security relies on essentially defect-free code, it also relies on human judgment about the methods used to secure the software. Subtle concurrency problems can't be reliably duplicated by running the code.
Once you are finished reading this book, you should be ready to
This book is organized in three parts.
I wrote the examples imagining a pair programming session. If you like looking at the map before wandering around, then you may want to go straight to the patterns in Part III and use the examples as illustrations. If you prefer just wandering around and then looking at the map to see where you've been, then try reading through the examples, referring to the patterns when you want more detail about a technique, and using the patterns as a reference. Several reviewers of this book commented they got the most out of the examples when they started up a programming environment, entered the code, and ran the tests as they read.
A note about the examples. Both of the examples, multi-currency calculation and a testing framework, appear simple. There are (and I have seen) complicated, ugly, messy ways of solving the same problems. I could have chosen one of those complicated, ugly, messy solutions, to give the book an air of "reality." However, my goal, and I hope your goal, is to write clean code that works. Before teeing off on the examples as being too simple, spend 15 seconds imagining a programming world in which all code was this clear and direct, where there were no complicated solutions, only apparently complicated problems begging for careful thought. TDD can help you to lead yourself to exactly that careful thought.
From the Back Cover
Clean code that works--now. This is the seeming contradiction that lies behind much of the pain of programming. Test-driven development replies to this contradiction with a paradox--test the program before you write it.
A new idea? Not at all. Since the dawn of computing, programmers have been specifying the inputs and outputs before programming precisely. Test-driven development takes this age-old idea, mixes it with modern languages and programming environments, and cooks up a tasty stew guaranteed to satisfy your appetite for clean code that works--now.
Developers face complex programming challenges every day, yet they are not always readily prepared to determine the best solution. More often than not, such difficult projects generate a great deal of stress and bad code. To garner the strength and courage needed to surmount seemingly Herculean tasks, programmers should look to test-driven development (TDD), a proven set of techniques that encourage simple designs and test suites that inspire confidence.
By driving development with automated tests and then eliminating duplication, any developer can write reliable, bug-free code no matter what its level of complexity. Moreover, TDD encourages programmers to learn quickly, communicate more clearly, and seek out constructive feedback.
Readers will learn to:
This book follows two TDD projects from start to finish, illustrating techniques programmers can use to easily and dramatically increase the quality of their work. The examples are followed by references to the featured TDD patterns and refactorings. With its emphasis on agile methods and fast development strategies, Test-Driven Development is sure to inspire readers to embrace these under-utilized but powerful techniques.
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Top Customer Reviews
The book is divided into three sections. The first two sections are each walkthroughs of the aforementioned sample projects using TDD. The third section is a collection of notes and useful tips to try to get the most out of TDD. If you've ever read anything from Beck, then you should be familiar with his style. If you haven't, Beck is an engaging enough writer, and the text flows smoothly and is fairly pleasant to read.
It would help to be familiar with some member of the xUnit family prior to reading this book. Beck uses Java and JUnit for the first section, but never really goes into discussing the JUnit API. Readers unfamiliar with xUnit may have no idea how to proceed with writing their own tests using one of these frameworks. True the API is simple enough that its functions may be ascertained simply by reading the code, but this is no reason not to provide explanation. The second sample project is an actual implementation of xUnit, so a bit more information may be gleaned here. Beck made the curious decision to use Python as the language of implementation for the second project, although he does provide explanation of the language's fundamentals. Finally, none of the sample projects are really complicated enough to do more than get us going on the path of TDD.Read more ›
The book start with example that involves teeny, weeny steps of test driven development that made me think this is really for people who don't know how to write test. And I consider myself to be a fully test-infected developer -- well, until I finally understand the idea that Kent is trying to convey here. It shows not only how to create a test case for a class, but also how to use test as the driving tool to assist refactoring for a better cleaner code. Becaus the way of development process is so much different from the normally way (well, depends on what you think is normally, isn't it), Kent carefully makes sure that the user doesn't get ahead of himself or herself. With little jokes here and little comments there, it really feels like being pair-programming with an XP mentor (it does, because I have been pair-programming with an XP mentor), who paitiently explains everything that is going on in his or her mind.
The second part of the book is also very unique. It goes through a process of using TDD to write a unit test framework. It shows, nicely, how to do TDD before the testing framework is in place, thus really tells what is the heart of TDD, and teaches a great lesson that TDD is not just writing test cases, but also a revolutionary development process.
The third part summrized patterns used in TDD, need I say more?
I think Beck does a good job in explaining test-driven development in a way that is easy to understand. I still have some concerns about the nature of test-driven development, such as the emphasis on function over design. But I think Beck achieved a reasonable goal of presenting by example what test-driven development is all about.
The goal of test-driven development is a reasonable way to achieve "clean code that works - now." As a tester, I think the awareness of test-driven development is a good thing. I also think that this technique must be combined with other methods, such as getting quality requirements, verification and validation, to achieve a final result that meets the users' needs.
Readability - 4
Coverage of topics - 5
Depth of coverage - 5
Credibility - 5
Accuracy - 5
Relevance to software quality - 5
Overall - 5
I was disappointed with the writing -- all of the little asides that were attempts at humor fell flat and were distracting. The biggest disappointment was that a chapter on how to integrate these techniques into the processes of a project, especially a large project, was ommitted.
At one point, the book states rather flippantly something to the effect that "You'll have to come up with your own argument to convince your boss to let you spend the time writing all these tests." I think that since he's the one promoting these techniques, he should be able to come up with those arguments. Personally, I think the argument is something like this:
- helps produce clean, modular code by forcing the designer to think about interfaces of the objects first. Coming up with good interfaces is half the battle.
- reduces defects tremendously because automated tests are available from the beginning and are used constantly.
- combines aspects of design and testing into the construction phase. So, the argument is that the "added" time spent writing tests saves time in the design and testing phases.
I would have also liked to have seen a section on the dangers of stubbed out code. Since the technique causes you to stub out a lot of methods, as you go through the process and people are fallable, it warrants discussion. Sometimes they forget that some of the code is stubbed. I've seen situations where stubbed out code (ie, return true) provided the correct answer for a surprisingly long time. It wasn't until it got into system testing that some of the less frequently encountered data caused mysterious problems to come up in supposedly working code.
Most recent customer reviews
Excellent book, you just must to take your time when you read it.Published 22 months ago by olaru victor
This is the source for TDD.
My only complaint is that the writing is sometimes too much a stream of thought. This can be difficult to understand and follow. Read more
I never really understood TDD before reading this book. A clear explanation, step-by-step with concrete examples, is what I needed to truly understand TDD. Read morePublished on Feb. 22 2013 by Pierre-Luc Maheu
The book is peppered with annoying digressions such as the following:
"When I was a young programmer- long, long ago when we had to dig our own bits out of the snow and... Read more
I like the way Kent Beck is doing is narrative inside the book. Of course it's less formal... but it's more comprehensive when you start. Read morePublished on April 27 2009 by Maxime Rouiller
This book does a remarkable job of covering the philosophy behind good unit tests and frequent automated builds. The author is very forward thinking in the ideas presented. Read morePublished on Jan. 18 2004
If you've never done or are curious about TDD, this is a great book to carefully walk you through learning how and why to do it. Read morePublished on Nov. 28 2003 by Lars Bergstrom
I bought this book for two reasons: it teaches TDD and it's spine has the thickness of a deck of cards. Read morePublished on Sept. 7 2003
I like the way Kent Beck writes his books. And it's sometimes thrilling to read his strange ideas. Having seen so many projects skip unit testing completely the idea of writing... Read morePublished on June 13 2003
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