1 Chapter 1- Introduction How Bugs affect our lives What is a Bug? What software testers do?

2 Examples of Bugs Disney's Lion King: 1994–1995 Disney company released its first multimedia CD-ROM game for children, T h e L i o n K i n g A n i m a t e d S t o r y b o o k. On December 26, the phone support technicians were swamped with calls from angry parents with crying children who couldn't get the software to work. Disney failed to test the software on a broad representation of the many different PC models available on the market. The software worked on a few systems—likely the ones that the Disney programmers used to create the game—

3 Examples of Bugs Intel Pentium Floating-Point Division Bug, 1994 Enter the following equation into your PC's calculator: ( / ) * – If the answer is zero, your computer is just fine. If you get anything else, you have an old Intel Pentium CPU with a floating-point division bug The way Intel handled the situation: –Their software test engineers had found the problem. Intel's management decided that the problem wasn't severe enough to fix it. –Once the bug was found, Intel attempted to diminish its perceived severity through press releases and public statements. –When pressured, Intel offered to replace the faulty chips, but only if a user could prove that he was affected by the bug.

4 Examples of Bugs NASA Mars Polar Lander, 1999 NASA's Mars Polar Lander disappeared during its landing. The planned landing: To save money….. What happened: Why: The lander was tested by multiple teams.

5 Examples of Bugs The Y2K (Year 2000) Bug, circa 1974 Very little memory for storage Shorten dates from their 4-digit format to a 2-digit format It's estimated that several hundred billion dollars were spent, worldwide, to replace or update computer programs to fix potential Year 2000 failures.

6 What Is a Bug? Terms for Software Failures –Defect –Variance –Fault –Failure –Problem –Inconsistency –Error –Feature –Incident –Bug –Anomaly

7 What Is a Bug? Fault, failure, and defect: imply a condition that's really severe or dangerous Anomaly, incident, and variance: unintended operation Problem, error, and bug: generic terms.

8 What Is a Bug? Companies differ in what they call bugs Some companies have different forms and procedures to handle different types of bugs DOD example

9 What Is a Bug? A software bug occurs when one or more of the following five rules is true: 1.The software doesn't do something that the product specification says it should do. 2.The software does something that the product specification says it shouldn't do. 3.The software does something that the product specification doesn't mention. 4.The software doesn't do something that the product specification doesn't mention but should. 5.The software is difficult to understand, hard to use, slow, or—in the software tester's eyes—will be viewed by the end user as just plain not right.

10 What Is a Bug? Apply the rules to Windows calculator Note about Rule 5: –It would be impossible to write software that every user thought was perfect. –As a software tester: be thorough, use your best judgment, and be reasonable

11 Why Do Bugs Occur?

12 Why Do Bugs Occur? 1.The number one cause of software bugs is the specification, why? –It is not written –It is not complete –It is not clear –It is constantly changing –It is not communicated well to the development team

13 Why Do Bugs Occur? 2.The next largest source of bugs is the design. (why?) 3.Coding errors –Software complexity –Poor documentation –Limited time –Programmer skills

14 Cost of Bugs

15 Cost of Bugs The costs are logarithmic: –A bug found and fixed during the early stages when the specification is being written might cost $1. –The same bug, if not found until the software is coded and tested, might cost $10 to $100. –If a customer finds it, the cost could easily be thousands or even millions of dollars. Note: apply to Disney Lion King case.

16 What Does a Software Tester Do? The goal of a software tester is to find bugs, find them as early as possible, and make sure they get fixed.

17 What Does a Software Tester Do? It's important to note that “fixing” a bug does not necessarily imply correcting the software. –It could mean adding a comment in the user manual –Providing special training to the customers. –It could require changing the statistics that the marketing group advertises –Postponing the release of the buggy feature

18 What Makes a Good Software Tester? Explorer: loves to get a new piece of software, install it and see what happens Troubleshooter: loves puzzles keep trying Make decisions about what to test and how long it will take? Diplomatic: bearer of bad news

19 What Makes a Good Software Tester? Creative Strive for perfection Persuasive: convenes management about the importance of a bug Software programming skills Expert in some non-computer field

20 Quiz 1.What's the goal of a software tester? 2.Give several reasons why the product specification is usually the largest source of bugs in a software product.