The Art of Software Testingby Glenford J. Myers, Myers
Provides a practical rather than theoretical discussion of the purpose and nature of software testing. Emphasizes methodologies for the design of effective test cases. Comprehensively covers psychological and economic principles, managerial aspects of testing, test tools, high-order testing, code inspections, and debugging. Extensive bibliography. Programmers at all levels, and programming students, will find this reference work indispensible.
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The Art of Software Testing
By Glenford J. Myers Corey Sandler Tom Badgett Todd M. Thomas
John Wiley & SonsISBN: 0-471-46912-2
Chapter OneA Self-Assessment Test
Since this book was first published 25 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 that have evolved. And, while relatively few people used computers in the 1970s, today virtually anyone in business or education could hardly complete a day's work without using a computer. Furthermore, the machines themselves are hundreds of times more powerful than those early 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 work or lost business. This is not to say that software is more important today than it was when the first edition of this book was published, but it is safe to say that computers-and the software that drives them-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 into applications without the need for a programmer to develop them from scratch. Graphical user interfaces (GUIs), forexample, can be built 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 much reduced.
Software testing is a process, or a series of processes, designed to make sure computer code does what it was designed to do and that it does not do anything unintended. Software should be predictable and consistent, offering no surprises to users. In this book we will look at many 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-to properly test a relatively simple program. Create a set of test data for the 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. The three values represent the lengths of the sides of a triangle. The program displays a message that states whether the triangle is scalene, isosceles, or equilateral.
Remember that a scalene triangle is one where no two sides are equal, whereas an isosceles triangle has two equal sides, and an equilateral triangle has three sides of equal length. Moreover, the angles opposite the equal sides in an isosceles triangle also are equal (it also follows 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 following questions. 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 not warrant a "yes" answer because there does not exist a triangle having 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 count because it is not a valid triangle.)
4. Do you have at least three test cases that represent valid isosceles 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?
6. Do you have a test case in which one side has a negative value?
7. Do you have a test case with three integers greater than zero such that the sum of two of the numbers is equal to the third? (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 that you have tried all three permutations where the length of one side is equal to the sum of the lengths of the other two sides (for example, 1,2,3; 1,3,2; and 3,1,2)?
9. Do you have a test case with three integers greater than zero such 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 that you have tried all three permutations (for example, 1,2,4; 1,4,2; and 4,1,2)?
11. Do you have a test case in which all sides are zero (0,0,0)? 12. Do you have at least one test case specifying noninteger values (such as 2.5,3.5,5.5)?
13. Do you have at least one test case specifying the wrong number of values (two rather than three integers, for example)?
14. For each test case did you specify the expected output from the program in addition to the input values?
Of course, a set of test cases that satisfies these conditions does not guarantee that all possible errors would be found, but since questions 1 through 13 represent errors that actually have occurred in different versions of this program, an adequate test of this program should expose at least these errors.
Now, before you become concerned about your own score, consider this: In our experience, highly qualified professional programmers score, on the average, only 7.8 out of a possible 14. If you've done better, congratulations; if not, we'll try to help.
The point of the exercise is to illustrate that the testing of even a trivial program such as this is not an easy task. And if this is true, consider the difficulty of testing a 100,000-statement air traffic control system, a compiler, or even a mundane payroll program. Testing also becomes more difficult with the object-oriented languages such as Java and C++. For example, your test cases for applications built with these languages must expose errors associated with object instantiation and memory management.
It might seem, from working with this example, that thoroughly testing a complex, real-world program would be impossible. Not so! Although the task can be daunting, adequate program testing is a very necessary-and achievable-part of software development, as you will learn in this book.
Excerpted from The Art of Software Testing by Glenford J. Myers Corey Sandler Tom Badgett Todd M. Thomas Excerpted by permission.
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Meet the Author
GLENFORD J. MYERS is a technology executive and a former senior staff member of IBM's Systems Research Institute, as well as the founder and former CEO of RadiSys Corporation.
TOM BADGETT has managed software development teams for large national corporations, has published more than sixty books in the computer hardware and software field, and served as technical editor for PCjr, Digital News, and other national computer magazines.
COREY SANDLER is one of the pioneers of computer journalism. He covered technology for Gannett Newspapers and the Associated Press and went on to become the first executive editor of PC Magazine. He also was the founding editor of Digital News, the newspaperfor DEC minicomputers. He has written more than 150 books on computers, business, and other topics.
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