In Favour of Test Driven Development
"It sounds very mechanical, but the effect is the exact opposite. What it does is free you to write. It liberates you to write."
John McPhee on having a system to write to.
"Art is freedom; and in art, as in life, there is no freedom without law."
Martin Amis on the importance of having rules and a code of conduct.
While referring to literature, these quotes resonate strongly with my feelings on writing software (JavaScript in particular) Imposing constraints on the process leads to greater clarity of thought. In writing: correct grammar, consistent style and brevity; in code: strict lint rules, clear design and, again, brevity.
Test Driven Development (TDD) is another self-imposed constraint. The following relates to a recent StackExchange Podcast, who's hosts are not enthusiastic about its supposed benefits and have evidence to back up their assertions.
"[...] a survey of all of the studies that have been done on TDD have shown that the better the study done, the weaker the signal as to its benefit."
A small concession is made that, for the majority of projects, TDD is poorly understood and executed. In which case I agree; used for its own sake or inappropriately: TDD has little value. For example, retrofitting unit tests misses the point entirely.
Used on functional, self-contained, code (JavaScript, perhapse) TDD provides constraining benefits that free the developer to solve their problem. Thinking about and exploring a solution is never a waste of effort, writing a test is a chance to frame a problem with greater clarity. Each test further tightens focus on the task. Each test is a tangible step forward, a possible break point and a starting point for the next push.
TDD has little benefit when interacting with existing APIs (DOM interactions, UI or web services). Only code, over which the developer has complete control (new, independent functions), can be discovered creatively. Otherwise the tests are simply a collection of roll-played guesses. The do not clarify the author's thoughts and intentions, instead they can easily reinforce her misconceptions.
"The fact is that everything I've written is very soon going to be absolutely nothing - and I mean nothing."
John McPhee, again, on leaving a legacy.
If it isn't providing satisfaction or feels like a drain on progress then TDD is counterproductive. In the hands of a developer who enjoys the process it becomes valuable aid.
