测试驱动开发（影印版）

.chapter 17: money retrospective
part ii: the xunit example
chapter 18: first steps to xunit
chapter 19: set the table
chapter 20: cleaning up after
chapter 21: counting
chapter 22' dealing with failure
chapter 23: how suite it is
chapter 24: xunit retrospective
part iii: patterns for test-driven development
chapter 25: test-driven development patterns
chapter 26: red bar patterns
chapter 27: testing patterns
chapter 28: green bar patterns
chapter 29: xunit patterns
chapter 30: design patterns
chapter 31: refactoring
chapter 32: mastering tdd
appendix i: influence diagrams
appendix ii: fibonacci
afterword
index

.　　 If the number of nasty surprises can be reduced enough, then project managers can estimate accurately enough to involve real customers in daily development.
　　 If the topics of technical conversations can be made clear enough, then software engineers can work in minute-by-minute collaboration instead of daily or weekly collaboration.
　　 Again, if the defect density can be reduced enough, then we can have shippable software with new functionality every day, leading to new business relationships with customers.
　　 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.
　　 Fear makes you tentative.
　　 Fear makes you want to communicate less.
　　 Fear makes you shy away from feedback.
　　 Fear makes you grumpy.
　　 None of these effects are helpful when programming, especially when programming something hard. So the question becomes how we face a difficult situation and,
　　 Instead of being tentative, begin learning concretely as quickly as possible.
　　 Instead of clamming up, communicate more clearly.
　　 Instead of avoiding feedback, search out helpful, concrete feedback.
　　 (You'll have to work on grumpiness on your own.)
　　 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 Ido 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 feed-back, 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
　　 Start simply
　　 Write automated tests
　　 Refactor to add design decisions one at a time
　　 This book is organized in three parts.
　　 Part I, The Money Example--An example of typical model code written using TDD. The example is one I got from Ward Cunningham years ago and have used many times since: multi-currency arithmetic. This example will enable you to learn to write tests before code and grow a design
　　 organically.
　　 Part II, The xUnit Example--An example of testing more complicated
　　 logic, including reflection and exceptions, by developing a framework for automated testing. This example also will introduce you to the xUnit
　　 architecture that is at the heart of many programmer-oriented testing tools. In the second example, you will learn to work in even smaller steps than in the first example, including the kind of self-referential hoo-ha beloved of computer scientists.
　　 Part III, Patterns for Test-Driven Development——Included are patterns for deciding what tests to write, how to write tests using xUnit, and a greatest- hits selection of the design patterns and refactorings used in the examples.
　　 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.