Method-level Bug Prediction: Problems and Promises

Fixing software bugs can be colossally expensive, especially if they are discovered in the later phases of the software development life cycle. As such, bug prediction has been a classic problem for the research community. As of now, the Google Scholar site generates similar to 113,000 hits if searched with the "bug prediction" phrase. Despite this staggering effort by the research community, bug prediction research is criticized for not being decisively adopted in practice. A significant problem of the existing research is the granularity level (i.e., class/file level) at which bug prediction is historically studied. Practitioners find it difficult and time-consuming to locate bugs at the class/file level granularity. Consequently, method-level bug prediction has become popular in the past decade. We ask, are these method-level bug prediction models ready for industry use? Unfortunately, the answer is no. The reported high accuracies of thesemodels dwindle significantly if we evaluate them in different realistic time-sensitive contexts. It may seem hopeless at first, but, encouragingly, we show that future method-level bug prediction can be improved significantly. In general, we show how to reliably evaluate future method-level bug prediction models and how to improve them by focusing on four different improvement avenues: building noise-free bug data, addressing concept drift, selecting similar training projects, and developing a mixture of models. Our findings are based on three publicly available method-level bug datasets and a newly built bug dataset of 774, 051 Java methods originating from 49 open-source software projects.