Research Supports The Effectiveness of TDD

From you've been HAACKED:

My favorite part of [a paper published in the Proceedings of the IEEE Transactions on Software Engineering entitled On the Effectiveness of Test-first Approach to Programming] is the section in which they offer their explanations for why they believe that Test-First programming might offer productivity benefits. I won’t dock them for using the word synergistic.

We believe that the observed productivity advantage of Test-First subjects is due to a number of synergistic effects:

• Better task understanding. Writing a test before implementing the underlying functionality requires the programmer to express the functionality unambiguously.
• Better task focus. Test-First advances one test case at a time. A single test case has a limited scope. Thus, the programmer is engaged in a decomposition process in which larger pieces of functionality are broken down to smaller, more manageable chunks. While developing the functionality for a single test, the cognitive load of the programmer is lower.
• Faster learning. Less productive and coarser decomposition strategies are quickly abandoned in favor of more productive, finer ones.
• Lower rework effort. Since the scope of a single test is limited, when the test fails, rework is easier. When rework immediately follows a short burst of testing and implementation activity, the problem context is still fresh in the programmer’s mind. With a high number of focused tests, when a test fails, the root cause is more easily pinpointed. In addition, more frequent regression testing shortens the feedback cycle. When new functionality interferes with old functionality, this situation is revealed faster. Small problems are detected before they become serious and costly.

Test-First also tends to increase the variation in productivity. This effect is attributed to the relative difficulty of the technique, which is supported by the subjects’ responses to the post-questionnaire and by the observation that higher skill subjects were able to achieve more significant productivity benefits.

So while I don’t expect that those who are resistant or disparaging of TDD will suddenly change their minds on TDD, I am encouraged by this result as it jives with my own experience. The authors do cite several other studies (future reading material, woohoo!) that for the most part support the benefits of TDD.

So while I’m personally convinced of the benefits of TDD and feel the evidence thus far supports that, I do agree that the evidence is not yet overwhelming. More research is required.

I prefer to take a provisional approach to theories, ready to change my mind if the evidence supports it. Though in this case, I find TDD a rather pleasant fun enjoyable method for writing code. There would have to be a massive amount solid evidence that TDD is a colossal waste of time for me to drop it.