Locating user functionality in old code

It is pointed out that software maintainers often have to recover requirements traceability in old code. In other words, they need to determine in which parts of the program the functionality X is implemented. The authors propose a methodology for answering this question based on the use of carefully designed test cases as probes into the code. While the methodology is not applicable to all kinds of requirements and may not find all relevant code components, it should often provide a maintainer with good starting points for studying a large and poorly documented system. Two formulations of the methodology are suggested, and some encouraging experimental results are presented from a case study of a typical old program.>