Applying TDD in principle if not in practice

My previous post was about describing the essence of TDD as a specification and direction tool, using non-technical examples. A quick recap: the point of TDD is to know where you going, and how to know when you’ve achieved your goal.

Several people have told me that TDD is all well and good, but it doesn’t apply to them, for various reasons. One chap told me he can’t to TDD because he’s a ‘SQL developer’ (his words). A friend told me he works on a vendor system, which is configured with XSLT files, and there is no tooling to support TDD. Its all very well to use whatever flavour of xUnit you want, but what about those who don’t have frameworks? What can the SQL, ASP and XSLT progammers and configurers out there do?

This is why it is important to understand the principle of TDD, and not only its practice (and why I think most demonstrations of TDD that I’ve seen focus too much on the practice).

As long as you have some way to set up a desired outcome, and can compare your actual outcome to your desired, you can perform TDD. You may not get some side benefits like automated regression testing and test coverage, but as mentioned in my previous post, those aren’t primary benefits. You also might not get the benefits of a decoupled design, since this may not make sense in your application.

You can still convey your intent. You will still have direction and focus. You will still be able to answer the question ‘am I done?’

A nice example of not getting the primary benefit of a decoupled design is the case of TDD in the SQL context. The team in which I’m currently working is still strongly focused on stored procedure and dataset-based programming. Therefore I’ve done a fair amount of thinking and playing in the TDD for SQL space. I’ve come up with a framework based on nUnit and TSQLUnit, but that’s another point.

I’ve used this framework to do TDD for stored procedures. One major shortcoming of T-SQL as a language (I feel dirty now) is that there’s no concept of abstraction. There is no way to break dependencies. If stored proceudre 1 (SP1) depends on user-defined function a (UDFa), there is no way I can test SP1 in isolation to UDFa. I therefore don’t get the benefit of a decoupled design, but I can still express the intent of my stored procedure, and I can prove when I’ve satisfied the requirment.

This is a clear case of the tooling failing the technique, but the technique can still be applied in principle. The same should be applicable in many other instances where there either isn’t tooling for the product (e.g. a vendor’s product which is configured).

Again, as long as you can create an expectation, and compare your actual outcome to that expectation, you can apply TDD in principle. So if you’ve previously had a look at TDD and wanted to apply it, but felt a lack of tooling for your particular case, think about how you can apply it in principle.


One thought on “Applying TDD in principle if not in practice

  1. This autumn I lectured a TDD course at the University of Helsinki and I applied the TDD way of thinking to the exercises: Each of the weekly exercises said that what you need to do to get the points. For example:

    “1 point: Out of FallingBlocksTest’s 10 tests 3 pass.
    2 points: Out of FallingBlocksTest’s 10 tests 6 pass.
    3 points: Out of FallingBlocksTest’s 10 tests 10 pass.”

    I think it worked quite well. The students could themselves decide that how much effort they would put into them, depending on how good grades they wanted from the course.

    (The exercises are at http://www.cs.helsinki.fi/u/luontola/tdd-2009/harjoitukset also in English. Use Google Translator for the rest.)

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