Test Driven Development (TDD) is Kent Beck's latest focus; the approach is proven to reduce defects and produce more robust software.
° Write clean code that works with the help of this groundbreaking software method
° Begin to write automated tests that allow you to "test on the fly," and learn to optimize the practice of refactoring
° Example-driven teaching; Kent Beck's step-by-step instruction will have you using TDD to further your projects
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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I. THE MONEY EXAMPLE.1. Multi-Currency Money.
II. The xUnit Example.18. First Steps to xUnit.
III. Patterns for Test-Driven Development.25. Test-Driven Development Patterns.
“Clean code that works” is Ron Jeffries’ pithy phrase. The goal is clean code that works, and for a whole bunch of reasons:
In Test-Driven Development, you:
Two simple rules, but they generate complex individual and group behavior. Some of the technical implications are:
The two rules imply an order to the tasks of programming:
1. Red—write a little test that doesn’t work, perhaps doesn’t even compile at first
2. Green—make the test work quickly, committing whatever sins necessary in the process
3. Refactor—eliminate all the duplication created in just getting the test to work
Red/green/refactor. The TDD’s mantra.
Assuming for the moment that such a style is possible, it might be possible to dramatically reduce the defect density of code and make the subject of work crystal clear to all involved. If so, writing only code demanded by failing tests also has social implications:
So, the concept is simple, but what’s my motivation? Why would a programmer take on the additional work of writing automated tests? Why would a programmer work in tiny little steps when their mind is capable of great soaring swoops of design? 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!”, 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, how can you 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 you get one test working, you know it is working, now and forever. You are one step closer to having everything working than you were when the test was broken. Now get the next one working, and the next, and the next. By analogy, the tougher the programming problem, the less ground should be covered by each test.
Readers of Extreme Programming Explained will notice a difference in tone between XP and TDD. TDD isn’t an absolute like Extreme Programming. 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 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 programmers learn TDD and go back to their earlier practices, reserving TDD for special occasions when ordinary programming isn’t making progress.
There are certainly 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 not sufficient to mechanically demonstrate that the goals of the software have been met. Security relies on essentially defect-free code, true, but also on human judgement 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 into three sections.
I wrote the examples imagining a pair programming session. If you like looking at the map before wandering around, you may want to go straight to the patterns in Section 3 and use the examples as illustrations. If you prefer just wandering around and then looking at the map to see where you’ve been, try reading the examples through and refering to the patterns when you want more detail about a technique, then using the patterns as a reference.
Several reviewers have commented they got the most out of the examples when they started up a programming environment and entered the code and ran the tests as they read.
A note about the examples. Both 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 is a practice that can help you lead yourself to exactly that careful thought.
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