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Test-driven development (TDD) is an agile software development approach that has been widely claimed to improve software quality. However, the extent to which TDD improves quality appears to be largely dependent upon the characteristics of the study in which it is evaluated (e.g., the research method, participant type, programming environment, etc.). The particularities of each study make the aggregation of results untenable. Objectives: The goal of this paper is to: increase the accuracy and generalizability of the results achieved in isolated experiments on TDD, provide joint conclusions on the performance of TDD across different industrial and academic settings, and assess the extent to which the characteristics of the experiments affect the quality-related performance of TDD. Method : We conduct a family of 12 experiments on TDD in academia and industry. We aggregate their results by means of meta-analysis. We perform exploratory analyses to identify variables impacting the quality-related performance of TDD. Results: TDD novices achieve a slightly higher code quality with iterative test-last development (i.e., ITL, the reverse approach of TDD) than with TDD. The task being developed largely determines quality. The programming environment, the order in which TDD and ITL are applied, or the learning effects from one development approach to another do not appear to affect quality. The quality-related performance of professionals using TDD drops more than for students. We hypothesize that this may be due to their being more resistant to change and potentially less motivated than students. Conclusion: Previous studies seem to provide conflicting results on TDD performance (i.e., positive vs. negative, respectively). We hypothesize that these conflicting results may be due to different study durations, experiment participants being unfamiliar with the TDD process, or case studies comparing the performance achieved by TDD vs. the control approach (e.g., the waterfall model), each applied to develop a different system. Further experiments with TDD experts are needed to validate these hypotheses.

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Context: The technical debt (TD) metaphor helps to conceptualize the pending issues and trade-offs made during software development. Knowing TD causes can support in defining preventive actions and having information about effects aids in the prioritization of TD payment. Goal: To investigate the impact of the experience level on how practitioners perceive the most likely causes that lead to TD and the effects of TD that have the highest impacts on software projects. Method: We approach this topic by surveying 227 practitioners. Results: While experienced software developers focus on human factors as TD causes and external quality attributes as TD effects, low experienced developers seem to concentrate on technical issues as causes and internal quality issues and increased project effort as effects. Missing any of these types of causes could lead a team to miss the identification of important TD, or miss opportunities to preempt TD. On the other hand, missing important effects could hamper effective planning or erode the effectiveness of decisions about prioritizing TD items. Conclusion: Having software development teams composed of practitioners with a homogeneous experience level can erode the team's ability to effectively manage TD.

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