Encyclopedia of Computer Science and Technology

Qquality assurance, softwareModern software programs are large and complex, and containmany interrelated modules. If a program is not thoroughlytested before it goes into service, it may containerrors that can result in serious consequences (see risks ofcomputing).In the early days of computing, programmers generallytested their code informally and nonsystematically. Theassumption was that after the program was given to the usersany problems that arose could be fixed through “patches”or replacement versions containing bug fixes. Today, however,it is increasingly recognized that assuring the qualityand reliability of software requires a systematic, comprehensiveprocess that begins when software requirements are firstspecified and continues after the program has been released.Any program is designed to meet the needs of a specifictype of users for specific applications. Therefore, thefirst step must be to make sure that users are able to communicatetheir requirements and that the software engineersunderstand the users’ needs and concerns. Detailedwritten specifications, flowcharts, and other depictions ofthe program can be reviewed by user representatives (seeflowchart and case). The specifications can be furtherexplored by creating a prototype or demonstration of theprogram’s features (see presentation software). Since aprototype can be dynamic and let users have simulatedinteractions with the program, it may reveal usability problemsthat would be hard to spot from charts or documentation.The result of this initial verification process shouldbe that the users agree that the program will do what theyneed and that they will be comfortable using it.In moving from design to implementation (writing theactual code), the developers must first choose an appropriateapproach (see algorithm) and data representation.Choosing an algorithm that is known to be sound is preferable,but if an algorithm must be modified (or a new onedeveloped), developers may be able to take advantage ofmathematical techniques that will suggest, if not totallyprove, the algorithm’s accuracy and reliability.As the programmers write the code, they should try touse best practices (see software engineering). Doing soensures that the code will be readable and organized insuch a way that the source of a problem area can be identifiedeasily, and any “fix” that must be made will be lesslikely to have unforeseen side effects.Developers can also include special code that will facilitatetesting. This code can include assertions—statements that testspecified conditions (such as variable values) at key points inthe program, displaying appropriate messages if the valuesare not within the proper range. Large, complex programscan also include diagnostic modules that give the developers asort of virtual console that they can use to monitor conditionswhile the program is running, or “drill into” particular areasfor closer inspection (see bugs and debugging).Although a certain amount of testing and debugging canand should be done while the code is being written, moreextensive and systematic testing is usually performed aftera preliminary version of the program has been completed.(This is sometimes called an alpha version.) There are twobasic approaches to designing the tests. “White box” tests usethe developer’s knowledge of the code to design test data thatwill test all of the program’s structural features (see proce-394