Analyzing the effects of test driven development in GitHub

Reviewed by Greg Wilson / 2021-09-16
Keywords: Test-Driven Development, Testing

Borle2017 is yet another study showing that test-driven development (TDD) doesn't have any significant impact. The authors looked at Java projects on GitHub for evidence of TDD, then looked for evidence that projects using TDD outperformed projects that didn't. Their conclusions: very few projects actually use it, and those that do don't perform any better than those that don't.

This is our sixth post about TDD, and the sixth time the conclusion has been that it doesn't make a difference. The studies we've discussed have used different methods and different datasets, but have all reached the same conclusion, so until we see a paper indicating that TDD does work, we're going to set this topic aside.

Borle2017 Neil C. Borle, Meysam Feghhi, Eleni Stroulia, Russell Greiner, and Abram Hindle: "Analyzing the effects of test driven development in GitHub". Empirical Software Engineering, 23(4), 2017, 10.1007/s10664-017-9576-3.

Testing is an integral part of the software development lifecycle, approached with varying degrees of rigor by different process models. Agile process models recommend Test Driven Development (TDD) as a key practice for reducing costs and improving code quality. The objective of this work is to perform a cost-benefit analysis of this practice. To that end, we have conducted a comparative analysis of GitHub repositories that adopts TDD to a lesser or greater extent, in order to determine how TDD affects software development productivity and software quality. We classified GitHub repositories archived in 2015 in terms of how rigorously they practiced TDD, thus creating a TDD spectrum. We then matched and compared various subsets of these repositories on this TDD spectrum with control sets of equal size. The control sets were samples from all GitHub repositories that matched certain characteristics, and that contained at least one test file. We compared how the TDD sets differed from the control sets on the following characteristics: number of test files, average commit velocity, number of bug-referencing commits, number of issues recorded, usage of continuous integration, number of pull requests, and distribution of commits per author. We found that Java TDD projects were relatively rare. In addition, there were very few significant differences in any of the metrics we used to compare TDD-like and non-TDD projects; therefore, our results do not reveal any observable benefits from using TDD.