Hira Agrawal

2 Computer Mining System Te s t s to Aid Software M a i n t e n a n c e B e f o re January 1, 2000, hundreds of millions of lines of legacy code must be understood, m o d i fied, and retested to avoid software fail-u res as the year changes from " 99 " to " 00. " This Year 2000 crisis is merely an acute phase of a chronic problem. Software engineers in general spend more than half their development time understanding, modifying, and retesting existing code. S o f t w a re companies have not tapped an import a n t re s o u rce in perf o rming these tasks. Most software development projects have a set of re g ression tests to help find bugs in the next release. But tests can be used for more than just finding errors. Modern test analysis tools can extract from these and other tests a wealth of information that can be useful in later software maintenance pro j e c t s. In this article, we describe techniques that main-tainers can use to enhance program understanding, debugging, and testing—the three most costly tasks in s o f t w a re maintenance. We have incorporated the techniques as part of Bellcore 's χSuds tool suite, a software understanding and diagnosis system. To show how analyzing tests can reveal valuable maintenance information in legacy software systems, we present examples from the Tag Value Object utility library, which is used in several Bellcore telecommunications systems. The TVO library re p resents, on a small scale, the typical complexities of legacy code. Like other systems which monitor test coverage, χSuds first creates a re p resentation of the pro g r a m 's c o n t rol graph, thus laying out its stru c t u re. As the maintainer runs various test cases, χSuds stores an execution trace, which re c o rds how many times each test has exercised a particular software component (function , block, decision, or dataflow association). E ffective use of χSuds re q u i res only that the main-tainer has a basic understanding of the pro g r a m 's feat u res and can identify the features each test case exercises. We discuss five χSuds tools that help maintainers exploit test data. …