Software testing by ron patton

Software Testing By Ron Patton

Chapter 1. Software Testing Background

• Infamous Software Error Case Studies
• What Is a Bug?
• Why Do Bugs Occur?
• The Cost of Bugs
• What Exactly Does a Software Tester Do?
• What Makes a Good Software Tester?

In 1947, computers were big, room-sized machines operating on mechanical relays and glowing vacuum tubes. The state of the art at the time was the Mark II, a behemoth being built at Harvard University. Technicians were running the new computer through its paces when it suddenly stopped working. They scrambled to figure out why and discovered, stuck between a set of relay contacts deep in the bowels of the computer, a moth. It had apparently flown into the system, attracted by the light and heat, and was zapped by the high voltage when it landed on the relay.
The computer bug was born. Well, okay, it died, but you get the point.
Welcome to the first chapter of Software Testing. In this chapter, you'll learn about the history of software bugs and software testing.
Highlights of this chapter include
• How software bugs impact our lives
• What bugs are and why they occur
• Who software testers are and what they do
Infamous Software Error Case Studies
It's easy to take software for granted and not really appreciate how much it has infiltrated our daily lives. Back in 1947, the Mark II computer required legions of programmers to constantly maintain it. The average person never conceived of someday having his own computer in his home. Now there's free software CD-ROMs attached to cereal boxes and more software in our kids' video games than on the space shuttle. What once were techie gadgets, such as pagers and cell phones, have become commonplace. Most of us now can't go a day without logging on to the Internet and checking our email. We rely on overnight packages, long-distance phone service, and cutting-edge medical treatments.
Software is everywhere. However, it's written by peopleso it's not perfect, as the following examples show.
Disney's Lion King, 1994-1995
In the fall of 1994, the Disney company released its first multimedia CD-ROM game for children, The Lion King Animated Storybook. Although many other companies had been marketing children's programs for years, this was Disney's first venture into the market and it was highly promoted and advertised. Sales were huge. It was "the game to buy" for children that holiday season. What happened, however, was a huge debacle. On December 26, the day after Christmas, Disney's customer support phones began to ring, and ring, and ring. Soon the phone support technicians were swamped with calls from angry parents with crying children who couldn't get the software to work. Numerous stories appeared in newspapers and on TV news.
It turns out that 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 gamebut not on the most common systems that the general public had.
Intel Pentium Floating-Point Division Bug, 1994
Enter the following equation into your PC's calculator:
(4195835 / 3145727) * 3145727 — 4195835

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 buga software bug burned into a computer chip and reproduced over and over in the manufacturing process.
On October 30, 1994, Dr. Thomas R.