Modernizing hierarchical delta debugging

Programmers tasked with the fixing of a bug prefer working on a minimal test case where every single bit is needed to reproduce the failure. However, cutting off the excess parts of a potentially large test case can be a tedious and time-consuming task if performed manually, which has led to the research and development of automated test case reduction techniques. The decade-old Hierarchical Delta Debugging (HDD) algorithm targets structured test inputs, parses them with the help of grammars and applies the minimizing Delta Debugging algorithm to the built trees. We have investigated this algorithm and its implementation, and propose improvements in this paper to address the found shortcomings. We argue that using extended context-free grammars with HDD is beneficial in several ways and the experimental evaluation of our modernized HDD implementation, called Picireny, supports the outlined ideas: the reduced outputs are significantly smaller (by circa 25-40%) on the investigated test cases than those produced by the reference HDD implementation using standard context-free grammars. These results, together with the technical improvements that ease the use of the modernized tool, can hopefully help spreading the adaptation of HDD in practice.