The art of software testing. Myers (2nd edition) (2004) (The art of software testing. Myers (2nd edition) (2004).pdf), страница 2

Rapid changes incomputer hardware and software technology during the 1980s and1990s necessitated frequent changes and updates to these topics.During that period dozens—perhaps even hundreds—of booksalso were published about software testing. They, too, took a moretransient approach to the topic.Myers’s The Art of Software Testing, on the other hand, gave theindustry a long-lasting, foundational guide to one of the most important computer topics: How do you ensure that all of the software youproduce does what it was designed to do and, just as important, doesnot do what it isn’t supposed to do?xixiiPrefaceThe version you are reading today retains that same foundationalphilosophy.

We have updated the examples to include more currentprogramming languages, and we have addressed topics that no oneknew about when Myers wrote the first edition: Web programming,e-commerce, and Extreme Programming and Testing.But we didn’t forget that a new classic must be true to its roots, sothis version also offers you a software testing philosophy that is allGlenford Myers, a philosophy and a process that work across currentand unforeseeable future hardware and software platforms. Hopefullythis, too, is a book that will span a generation of software designersand developers.IntroductionAt the time this book was firstpublished, in 1979, it was a well-known rule of thumb that in a typical programming project approximately 50 percent of the elapsedtime and more than 50 percent of the total cost were expended intesting the program or system being developed.Today, a quarter of the century later, the same is still true.

Thereare new development systems, languages with built-in tools, and programmers who are used to developing more on the fly. But testingstill plays an important part in any software development project.Given these facts, you might expect that by this time program testing would have been refined into an exact science. This is far fromtrue. In fact, less seems to be known about software testing thanabout any other aspect of software development. Furthermore, testing has been an out-of-vogue subject—it was true when this bookwas first published and, unfortunately, it is still true today. Today thereare more books and articles about software testing, meaning that, atleast, the topic has more visibility than it did when this book was firstpublished. But testing remains among the “dark arts” of softwaredevelopment.This would be more than enough reason to update this book onthe art of software testing, but there are additional motivations.

Atvarious times, we have heard professors and teaching assistants say,“Our students graduate and move into industry without any substantial knowledge of how to go about testing a program. Moreover, werarely have any advice to provide in our introductory courses on howa student should go about testing and debugging his or her exercises.”xiiixivIntroductionSo, the purpose of this updated edition of The Art of Software Testing is the same as it was in 1979: to fill these knowledge gaps for theprofessional programmer and the student of computer science.

As thetitle implies, the book is a practical, rather than theoretical, discussionof the subject, complete with updated language and process discussions. Although it is possible to discuss program testing in a theoretical vein, this book is intended to be a practical, “both feet on theground” handbook.

Hence, many subjects related to program testing,such as the idea of mathematically proving the correctness of a program, were purposefully excluded.Chapter 1 is a short self-assessment test that every reader shouldtake before reading further. It turns out that the most important practical information that you must understand about program testing isa set of philosophical and economic issues; these are discussed inChapter 2. Chapter 3 discusses the important concept of noncomputer-based code walk-throughs or inspections. Rather thanfocus attention on the procedural or managerial aspects of this concept, as most discussions do, Chapter 3 discusses it from a technical,how-to-find-errors point of view.The knowledgeable reader will realize that the most importantcomponent in the bag of tricks of a program tester is the knowledgeof how to write effective test cases; this is the subject of Chapter 4.Chapters 5 and 6 discuss, respectively, the testing of individual modules or subroutines and the testing of larger entities, with Chapter 7presenting some practical advice on program debugging.

Chapter 8discusses the concepts of extreme programming and extreme testing,while Chapter 9 shows how to use other features of program testingdetailed elsewhere in this book with Web programming, includinge-commerce systems.This book has three major audiences. Although we hope that noteverything in this book will be new information to the professionalprogrammer, it should add to the professional’s knowledge of testingtechniques. If the material allows you to detect just one more bug inone program, the price of the book will have been recovered manytimes over.

The second audience is the project manager, since thebook contains new, practical information on the management of theIntroductionxvtesting process. The third audience is the programming or computerscience student; the goal here is to expose the student to the problemsof program testing and to provide a set of effective techniques. It issuggested that the book be used as a supplement in programmingcourses such that the student is exposed to the subject of softwaretesting at an early time in his or her education.Glenford J. MyersTom BadgettTodd M.

ThomasCorey SandlerThe Art ofSoftwareTestingCHAPTER 1A Self-Assessment TestSince this book was first published25 years ago, software testing has become both easier and more difficult than ever.Software testing is more difficult because of the vast array of programming languages, operating systems, and hardware platforms thathave evolved.

And, while relatively few people used computers in the1970s, today virtually anyone in business or education could hardlycomplete a day’s work without using a computer. Furthermore, themachines themselves are hundreds of times more powerful than thoseearly devices.Therefore, the software we write today potentially touches millions of people, enabling them to do their jobs effectively and efficiently—or causing them untold frustration and the cost of lost workor lost business. This is not to say that software is more importanttoday than it was when the first edition of this book was published,but it is safe to say that computers—and the software that drivesthem—certainly affect more people and more businesses today.Software testing is easier, in some ways, because the array of software and operating systems is much more sophisticated than ever,providing intrinsic well-tested routines that can be incorporated intoapplications without the need for a programmer to develop themfrom scratch.

Graphical user interfaces (GUIs), for example, can bebuilt from a development language’s libraries, and, since they are preprogrammed objects that have been debugged and tested previously,the need for testing them as part of a custom application is muchreduced.Software testing is a process, or a series of processes, designed tomake sure computer code does what it was designed to do and that it12The Art of Software Testingdoes not do anything unintended. Software should be predictable andconsistent, offering no surprises to users.

In this book we will look atmany approaches to achieving this goal.Now, before we start the book, we’d like you to take a short exam.We want you to write a set of test cases—specific sets of data—toproperly test a relatively simple program. Create a set of test data forthe program—data the program must handle correctly to be considered a successful program. Here’s a description of the program:The program reads three integer values from an input dialog. Thethree values represent the lengths of the sides of a triangle.

Theprogram displays a message that states whether the triangle is scalene,isosceles, or equilateral.Remember that a scalene triangle is one where no two sides areequal, whereas an isosceles triangle has two equal sides, and an equilateral triangle has three sides of equal length. Moreover, the anglesopposite the equal sides in an isosceles triangle also are equal (it alsofollows that the sides opposite equal angles in a triangle are equal),and all angles in an equilateral triangle are equal.Evaluate your set of test cases by using it to answer the followingquestions.

Give yourself one point for each “yes” answer.1. Do you have a test case that represents a valid scalene triangle? (Note that test cases such as 1,2,3 and 2,5,10 do notwarrant a “yes” answer because there does not exist a trianglehaving these dimensions.)2.

Do you have a test case that represents a valid equilateral triangle?3. Do you have a test case that represents a valid isosceles triangle? (Note that a test case representing 2,2,4 would not countbecause it is not a valid triangle.)4. Do you have at least three test cases that represent validisosceles triangles such that you have tried all three permutations of two equal sides (such as, 3,3,4; 3,4,3; and 4,3,3)?5.

Do you have a test case in which one side has a zero value?A Self-Assessment Test36. Do you have a test case in which one side has a negativevalue?7. Do you have a test case with three integers greater than zerosuch that the sum of two of the numbers is equal to thethird? (That is, if the program said that 1,2,3 represents a scalene triangle, it would contain a bug.)8. Do you have at least three test cases in category 7 such thatyou have tried all three permutations where the length ofone side is equal to the sum of the lengths of the other twosides (for example, 1,2,3; 1,3,2; and 3,1,2)?9. Do you have a test case with three integers greater than zerosuch that the sum of two of the numbers is less than the third(such as 1,2,4 or 12,15,30)?10. Do you have at least three test cases in category 9 such thatyou have tried all three permutations (for example, 1,2,4;1,4,2; and 4,1,2)?11.