Debugging the Undebuggable: Why Multi-Fault Programs Break Debugging and Repair Tools

Multi-fault programs, which contain more than one bug simultaneously, are notoriously difficult to debug and repair. This is largely because faults can interact in subtle ways: one might hide the effects of another, or even cause new failures to appear when combined. In this paper, we investigate why multi-fault programs remain so challenging for today’s debugging and repair tools. We introduce a formal model that captures the different ways faults can interact, including masking, synergy, and cascading. Building on this model, we propose a novel framework for reasoning about faults, not in isolation, but as part of a network of influences. This perspective opens the door for future tools that can better understand, diagnose, and repair programs with multiple faults.