I remember being introduced to Test Driven Development (TDD) very well. This is because it had such an overwhelming change on how I write code day to day. It was incredibly alien, difficult, yet rewarding. On this journey for the last five years I've changed my style, learned how not to do it and finally found my "sweet spot" when it comes to pragmatic TDD.
Writing code is fun. Developing an application or system is fun. Using new technology is fun. Despite this the end goal should always be to deliver value. Delivering business value over religiously following a practice was a turning point in my journey. After all the user doesn't care about what is behind the scenes, as long as they can use your software, they're happy.
When to Write Tests?
One of the guidelines when starting TDD is
"Never write a line of code without a failing test" - Kent Beck
This rule is wrong on many levels. Firstly it cripples most developers when starting TDD. Secondly the guideline is broken all the time by seasoned evangelists. Writing some framework code? Writing data access code? Writing markup? Any of these scenarios would be wasted by writing a failing tests first. This rule should be reworded.
"Writing logic? Never write a line of code without a failing test" - me
It's OK to not use TDD
After adoption TDD practitioners tend to face two challenges. Other developers looking down on non TDD practices and feeling as if they are "cheating" when not using TDD. The later was an issue I struggled with. Newbies tend to find the same problem, and this goes back to the mantra above. One of the key lessons I've discovered over the past few years is that using TDD where appropriate is fine. Not all code needs TDD. Even Kent Beck discusses this when he refers to "Obvious Implementation".
Another game changer in my journey was the concept of "Spike and Stabilize". Using this technique you can deliver business value quickly. Gather feedback as soon as possible and either fail fast or wrap the code in tests and clean it up.
Most of the code I (and others) write is very similar. I'd bet this is the same for different fields of software development. That being said, for each CRUD app we create there is a tiny aspect of this that is unique. Using TDD to write yet another CRUD app is tedious. I'd imagine this is why many ditch the practice of TDD after some time. However the benefit comes from using TDD for that 20% of domain logic. Here a combination of obvious implementation and spike and stabilize can assist in the creation of the other 80%.
It's about Design too
TDD by Example gives the impression that the practice is primarily a testing discipline. This is not true. TDD does limit the bugs I introduce and enforces basic correctness, however bugs will still slip through. After all the quality of the code is only as good as the quality of the tests. Growing Object Oriented Software: Guided by Tests and others introduce the concept that TDD is also a design process. Listening to the tests is a core concept. In other words, if something is hard to test, chances are the code in question can be improved.
Follow the Risks
The final lesson I've come to realise is that even if you happen to work with those who don't practice TDD, you can reap the benefits. Simply test where the risk lives. Ignore the framework, standard library and simply test what has risk. This might be a small, core part of your application. Aiming for 100% code coverage is not a goal, nor one worth aiming for.
It's a Tool
At the end of the day, TDD is a tool, not a goal. In this day and age many believe that TDD should be mandatory. While I agree, the use should be restricted to where and when it makes sense. As for when and where, this is up for the developer to decide. Using some of the findings above allow me to be pragmatic, yet still have confidence in the quality of my code.