One of the distinguishing characteristics of software systems is that they evolve: new patches are committed to software repositories and new versions are released to users on a continuous basis. Unfortunately, many of these changes bring unexpected bugs that break the stability of the system or act its security. In this paper, we address this problem using a technique for automatically testing code patches. Our technique combines symbolic execution with several novel heuristics based on static and dynamic program analysis which allow it to quickly reach the code of the patch. We have implemented our approach in a tool called KATCH, which we have applied to all the patches written in a combined period of approximately six years for nineteen mature programs from the popular GNU diffutils, GNU binutils and GNU findutils utility suites, which are shipped with virtually all UNIX-based distributions. Our results show that KATCH can automatically synthesise inputs that significantly increase the patch coverage achieved by the existing manual test suites, and find bugs at the moment they are introduced.
Conference talk at ESEC/FSE 2013.