(No) Influence of Continuous Integration on the Commit Activity in GitHub Projects

TL;DR

This empirical study investigates whether the adoption of Continuous Integration (CI) influences commit activity in GitHub projects, finding minimal effects and emphasizing the importance of baseline comparisons.

Contribution

The paper provides an empirical analysis showing that CI adoption does not significantly alter commit activity, highlighting the need for baseline comparisons in such studies.

Findings

Increased merge ratio after CI adoption, but also in non-CI projects.

No significant change in overall commit activity post-CI.

Baseline comparison is crucial to attribute effects correctly.

Abstract

A core goal of Continuous Integration (CI) is to make small incremental changes to software projects, which are integrated frequently into a mainline repository or branch. This paper presents an empirical study that investigates if developers adjust their commit activity towards the above-mentioned goal after projects start using CI. We analyzed the commit and merge activity in 93 GitHub projects that introduced the hosted CI system Travis CI, but have previously been developed for at least one year before introducing CI. In our analysis, we only found one non-negligible effect, an increased merge ratio, meaning that there were more merging commits in relation to all commits after the projects started using Travis CI. This effect has also been reported in related work. However, we observed the same effect in a random sample of 60 GitHub projects not using CI. Thus, it is unlikely that the effect is caused by the introduction of CI alone. We conclude that: (1) in our sample of projects, the introduction of CI did not lead to major changes in developers' commit activity, and (2) it is important to compare the commit activity to a baseline before attributing an effect to a treatment that may not be the cause for the observed effect.