Test Driven is a loaded term and means different things to different people. I much prefer the term Test First which clearly states that the test comes before the implementation. However, for me, the value is not necessarily in creating an executable test, but in the thought processes that Test First brings out.
One of my colleagues at emergn is constantly reminding me that when presented with a solution you need to ask yourself what is the problem. This is what lead me to question TDD and it’s variants. If you search the web for Test Driven Development, you’ll uncover a wealth of information from many of the authors in my BlogRoll, as well as many variants on a theme. I think the wikipedia entry is a particularly good summary of Test Driven as it is currently understood by the community but for the real meat and bones you need to look at the articles from the thought leaders behind the practises.
However, when I look at this wealth of information, I’m now faced with the question… OK, these are all solutions, but what is the fundamental problem they are solving? Is it
- Code quality/design is poor
- Code is overly complex/difficult to test
- Unused functionality within the code
- Too many bugs
It is only when we understand the underlying problem fully that we can then evaluate the applicability/suitability of a particular approach. Indeed, it is this lack of a clearly defined problem which makes it impossible to determine which approach is best, since we can’t define any tests up front… This is actually a little bit of a paradox, but highlights for me one of the most important points about TDD. TDD is a solution to too many problems and in certain cases is not a very good solution.
Testing should be about proving functionality, but unfortunately we too often see TDD trying to address non testing issues like design and code quality. Of course, code needs to be testable, but it is not the responsibility of the Testing to enforce this, it is the responsibility of the design, but this is (unfortunately IMHO) the missing piece in most methodologies… Indeed, the approach of writing the “Simplest Possible Thing” to pass a test is possibly my biggest bug-bear with TDD. This approach often means you can pass tests with no functionality other than hard coded return values, now that has to be the biggest process smell ever.
I’m going to stop using TDD, or Test Driven now and use instead the term I prefer which is Test First. For me, this means that before I do anything, I will determine ahead of time how I would test it. The immediate benefit (a.k.a value) I get from determining how to test something is I’m also starting to think about (dare I suggest design) things like apis/design/interaction/responsibilities. This is not the same as BDUF (big design up front), instead it is just enough thought at just the right moment to (hopefully) prevent a disaster. I can then apply some cost/benefit analysis with a pinch of risk analysis to assign a value to actually writing all the tests that TDD would have forced you to write, or just a small percentage to cover the important or more complex functionality.
Of course, in many cases I will actually create executable tests for many of those uncovered during this thought exercise, but will I go through the whole Red/Green/Refactor cycle, possibly not. For me the Red/Green/Refactor is like micro context switching. I prefer a slightly longer period of focus and therefore I may write quite a few tests at the same time before applying that context switch to go into coding mode. This of course is my personal preference and undoubtedly would be scorned upon by the dogmatic TDD zealots, but if this is what makes me more productive, and without a baseline problem statement I challenge them to prove that this is not the best way to do your testing.
Test First allows me to
- Understand the problem I’m trying to solve
- Think about how I will solve it (just enough design)
- Uncover any unknowns or risks hidden in the initial problem statement
- Produce high quality code which has just enough tests
Many of the Test Driven approaches do indeed address many of the initial problems stated earlier, but are they the only solution to these problems? Indeed, are these problems actually just symptoms of even deeper problems? If the problem is simply that your code is very tightly coupled and difficult to test then the best ROI will probably come not from TDD but from up-skilling your development team on fundamental design principles (unskilled developers was the real problem in the first place and TDD can’t solve that).
- Wikipedia entry for Test Driven Development: http://en.wikipedia.org/wiki/Test-driven_development
- Introducing BDD by Dan North: http://dannorth.net/introducing-bdd (highly recommended reading)
- C2 wiki entry for Test Driven: http://c2.com/cgi/wiki?TestDriven