It Will Never Work in Theory

Test-Driven Development

Posted Oct 5, 2016 by Greg Wilson

| Testing |

Davide Fucci, Giuseppe Scanniello, Simone Romano, Martin Shepperd, Boyce Sigweni, Fernando Uyaguari, Burak Turhan, Natalia Juristo, and Markku Oivo: "An External Replication on the Effects of Test-driven Development Using a Multi-site Blind Analysis Approach". ESEM 2016,

Context: Test-driven development (TDD) is an agile practice claimed to improve the quality of a software product, as well as the productivity of its developers. A previous study (i.e., baseline experiment) at the University of Oulu (Finland) compared TDD to a test-last development (TLD) approach through a randomized controlled trial. The results failed to support the claims. Goal: We want to validate the original study results by replicating it at the University of Basilicata (Italy), using a different design. Method: We replicated the baseline experiment, using a crossover design, with 21 graduate students. We kept the settings and context as close as possible to the baseline experiment. In order to limit researchers bias, we involved two other sites (UPM, Spain, and Brunel, UK) to conduct blind analysis of the data. Results: The Kruskal-Wallis tests did not show any significant difference between TDD and TLD in terms of testing effort (p-value = .27), external code quality (p-value = .82), and developers’ productivity (p-value = .83). Nevertheless, our data revealed a difference based on the order in which TDD and TLD were applied, though no carry over effect. Conclusions: We verify the baseline study results, yet our results raises concerns regarding the selection of experimental objects, particularly with respect to their interaction with the order in which of treatments are applied.

This painstaking study is the latest in a long line to find that test-driven development (TDD) has little or no impact on development time or code quality. Here, the authors repeated an earlier study with a couple of new wrinkles, and then blinded their data before giving it to someone else to analyze to remove any possibility of bias. The result: no significant difference between TDD and iterative test-last (ITL) development.

...which still surprises me seven years after Turhan et al's meta-analysis in Making Software. reported the same result. I don't program very much any more, but when I do, I feel that writing tests up front makes me more productive. I'd like to be able to say that these researchers and others must be measuring the wrong things, or measuring things the wrong way, but after so many years and so many different studies, those of us who believe might just have to accept that our self-assessment is wrong.

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