Neuron coverage criteria were a placebo for finding LLM bugs: erroneous samples added only 0.32 percent coverage over noise, and coverage guidance raised adversarial sample yield by 4.56 percent
AspireAI community · arXiv
Neuron coverage criteria are used to judge test-suite quality and guide test-input generation, but their value for transformer-based language models was unclear. This study, published in ACM Transactions on Software Engineering and Methodology, evaluates six criteria across encoder-only, decoder-only and encoder-decoder models. Erroneous samples provided only 0.32 percent additional coverage over noise samples, indicating weak sensitivity to adversarial errors, while the criteria did assess distribution diversity and sample fairness in 26 and 30 of 33 configurations respectively. Adding neuron-wise coverage guidance to test-input generation increased adversarial sample production by only 4.56 percent. The authors conclude the criteria can work as an antidote for measuring diversity but remain largely a placebo for revealing adversarial errors, particularly when used one criterion at a time, and that their value depends on whether that limited benefit justifies the computational overhead.
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