The ideas and techniques of software testing have become essential knowledge for all software developers. A software developer can expect to use the concepts presented in this book many times during his or her career. This chapter introduces the subject of software testing by describing the activities of a test engineer, defining a number of key terms, and then explaining the central notion of test coverage.

Software is a key ingredient in many of the devices and systems that pervade our society. Software defines the behavior of network routers, financial networks, telephone switching networks, the Web, and other infrastructure of modern life. Software is an essential component of embedded applications that control exotic applications such as airplanes, spaceships, and air traffic control systems, as well as mundane appliances such as watches, ovens, cars, DVD players, garage door openers, cell phones, and remote controllers. Modern households have over 50 processors, and some new cars have over 100; all of them running software that optimistic consumers assume will never fail! Although many factors affect the engineering of reliable software, including, of course, careful design and sound process management, testing is the primary method that the industry uses to evaluate software under development. Fortunately, a few basic software testing concepts can be used to design tests for a large variety of software applications. A goal of this book is to present these concepts in such a way that the student or practicing engineer can easily apply them to any software testing situation.