Supporting the regression testing in Lisp programs

How often have you made a change in a system to fix a bug or add a feature and been totally sure that the change did not affect anything else, only to discover weeks or months later tha t the change broke something? In my personal experience, the single most valuable software maintenance tool is a regression tester, which maintains a suite of tests for a system and can run them automatical ly when the system is changed. The term "regression testing" is used, because each version of the system being tested is compared with the previous version to make sure that the new version has not regressed by losing any of the tested capabilities. The more comprehensive the test suite is, the more valuable this comparison becomes. Creating a comprehensive test suite for a system requires significant effort, and running a test suite can require significant amounts of computer time. However, given a comprehensive test suite, regression testing detects an impressive number of bugs with remarkably little human effort. The KT regression tester presented here supports the regression testing of systems wri t ten in Common Lisp. In addition to being a valuable tool, RT is an interesting example of the power of Lisp. The unified nature of the Lisp programming environment and the fact that Lisp programs can be manipulated as da ta allows RT to be implemented in two pages of code. Merely implement ing a batch-mode regression tester using an Algol-like language in a typical programming environment would require much more code. Implement ing a highly interactive system like RT would be a major undertaking. U s e r ' s M a n u a l for RT