What Makes Testing Work: Nine Case Studies of Software Development Teams

Recently there has been a focus on test first and test driven development; several empirical studies have tried to assess the advantage that these methods give over testing after development. The results have been mixed. In this paper we investigate nine teams who tested during coding to examine the effect it had on the external quality of their code. Of the top three performing teams two used a documented testing strategy and the other an ad-hoc approach to testing. We conclude that their success appears to be related to a testing culture where the teams proactively test rather than carry out only what is required in a mechanical fashion.