Quality of Testing in Test Driven Development

Test-driven development is an essential part of Extreme Programming approach with the preference of being followed in other Agile methods as well. For several years, researchers are performing empirical investigations to evaluate quality improvements in the resulting code when test-driven development is being used. However, very little had been reported into investigating the quality of the testing performed in conjunction with test-driven development. In this paper we present results from an experiment specifically designed to evaluate the quality of test cases created by developers who used the test-first and the traditional test-last approaches. On an average, the quality of testing in test-driven development was almost the same as the quality of testing using test-last approach. However, detailed analysis of test cases, created by test-driven development group, revealed that 29% of test cases were "negative" test cases (based on non-specified requirements) but contributing as much as 65% to the overall tests quality score of test-first developers. We are currently investigating the possibility of extending test driven development to facilitate non-specified requirements to a higher extent and thus minimise the impact of a potentially inherent effect of positive test bias.