Conformance factor in test-driven development: initial results from an enhanced replication

Test-driven development (TDD) is an iterative software development technique where unit-tests are defined before production code. The proponents of TDD claim that it improves both external quality and developers' productivity. In particular, Erdogmus et al. (i.e., original study) proposed a two-stage model to investigate these claims regarding TDD's effects. Our aim is to enhance the model proposed in the original study by investigating an additional factor: TDD process conformance. We conducted a close, external replication of the original study accompanied by a correlation analysis to check whether process conformance is related to improvements for the subjects using TDD. We partially confirmed the results of the original study. Moreover, we observed a correlation between process conformance and quality, but not productivity. We found no evidence to support the claim that external quality and productivity are improved by the adoption of TDD compared to test-last development. Finally, conformance to TDD process improves the quality and does not affect productivity. We conclude that the role of process conformance is relevant in studying the quality and productivity-related effects of TDD.