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The research we base our work on. By learning from others who follow the scientific method, we are able to better determine what really works and learn from their experiments.

Featured Research
North Carolina State University
Realizing quality improvement through test driven development: results and experiences of four industrial teams
Nachiappan Nagappan & E. Michael Maximilien & Thirumalesh Bhat & Laurie Williams
Test-driven development (TDD) is a software development practice that has been used sporadically for decades. With this practice, a software engineer cycles minute-by-minute between writing failing unit tests and writing implementation code to pass those tests. Testdriven development has recently re-emerged as a critical enabling practice of agile software development methodologies. However, little empirical evidence supports or refutes the utility of this practice in an industrial context. Case studies were conducted with three development teams at Microsoft and one at IBM that have adopted TDD. The results of the case studies indicate that the pre-release defect density of the four products decreased between 40% and 90% relative to similar projects that did not use the TDD practice. Subjectively, the teams experienced a 15-35% increase in initial development time after adopting TDD.learn more
VTT Technical Research Centre of Finland
A Comparative Case Study on the Impact of Test-Driven Development on Program Design and Test Coverage
Siniaalto, M., & Abrahamsson P
Test-driven development (TDD) is a programming technique in which the tests are written prior to the source code. It is proposed that TDD is one of the most fundamental practices enabling the development of software in an agile and iterative manner. Both the literature and practice suggest that TDD practice yields several benefits. Essentially, it is claimed that TDD leads to an improved software design, which has a dramatic impact on the maintainability and further development of the system. The impact of TDD on program design has seldom come under the researchers' focus. This paper reports the results from a comparative case study of three software development projects where the effect of TDD on program design was measured using object oriented metrics. The results show that the effect of TDD on program design was not as evident as expected, but the test coverage was significantly superior to iterative test-last development.learn more
North Carolina State University
An Initial Investigation of Test Driven Development in Industry
Boby George, & Laurie Williams
Test Driven Development (TDD) is a software development practice in which unit test cases are incrementally written prior to code implementation. In our research, we ran a set of structured experiments with 24 professional pair programmers. One group developed code using TDD while the other a waterfall-like approach. Both groups developed a small Java program. We found that the TDD developers produced higher quality code, which passed 18% more functional black box test cases. However, TDD developer pairs took 16% more time for development. A moderate correlation between time spent and the resulting quality was established upon analysis. It is conjectured that the resulting high quality of code written using the TDD practice may be due to the granularity of TDD, which may encourage more frequent and tighter verification and validation. Lastly, the programmers which followed a waterfall-like process often did not write the required automated test cases after completing their code, which might be indicative of the tendency among practitioners toward inadequate testing. This observation supports that TDD has the potential of increasing the level of testing in the industry as testing as an integral part of code development.learn more
National Institute for Space Research, São José dos Campos, Brazil
Federal University of São Paulo
Developers' Initial Perceptions on TDD Practice: A Thematic Analysis with Distinct Domains and Languages
Joelma Choma, Eduardo M. Guerra, & Tiago Silva da Silva
Test-Driven Development (TDD) is one of the most popular agile practices among software developers. To investigate the software developers’ initial perceptions when applying TDD, we have performed an exploratory study. This study was carried out with participants who had about ten years of professional experience (on average), the majority of whom with no experience using TDD. The study is in the context of an agile project course at the postgraduate level of a research institute. Participants individually developed medium size projects addressed to different domains and using different programming languages. Through a structured questionnaire with open and semi-open questions, we collected information on TDD effects such as the perceived benefits, encountered difficulties, and developer’s opinion about the quality improvement of the software. Afterward, we conducted a thematic analysis of the qualitative data. Most participants noticed improvements in code quality, but few have a more comprehensive view of the effects of TDD on software design. Our findings suggest that after overcoming the initial difficulties to understand where to start, and know how to create a test for a feature that does not yet exist, participants gain greater confidence to implement new features and make changes due to broad test coverage.learn more
IEEE Transactions on Software Engineering
The Effects of Test-Driven Development on External Quality and Productivity: A Meta-Analysis
Yahya Rafique and Vojislav B. Misic, Senior Member, IEEE
Abstract—This paper provides a systematic meta-analysis of 27 studies that investigate the impact of Test-Driven Development (TDD) on external code quality and productivity. The results indicate that, in general, TDD has a small positive effect on quality but little to no discernible effect on productivity. However, subgroup analyses have found both the quality improvement and the productivity drop to be much larger in industrial studies in comparison with academic studies. A larger drop of productivity was found in studies where the difference in test effort between the TDD and the control group’s process was significant. A larger improvement in quality was also found in the academic studies when the difference in test effort is substantial, however, no conclusion could be derived regarding the industrial studies due to the lack of data. Finally, the influence of developer experience and task size as moderator variables was investigated, and a statistically significant positive correlation was found between task size and the magnitude of the improvement in quality.learn more

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