Looking for a New Year's Resolution?

There are many exciting .NET topics waiting for us in 2004. Simply too much stuff to be tried and understood, too much knowledge to be gained. If you're making plans for 2004, here's one single thing I can fully recommend:

If you're not already doing it, start writing unit tests using a test framework.

Unit testing is one of these "I really should be doing this" concepts. Even though I read and heard about unit testing years ago, I only started doing it in 2003. Sure, I always had some kind of test applications for e.g. a library - who hasn't written one of those infamous programs consisting of a form and dozens of buttons ("button1", "button2", ...), each starting some test code. And it's not as if my software was of poor quality. But looking back, unit testing was the thing in 2003 that made me a better developer.

I'm using NUnit for my unit tests; it's so easy to use that a typical reaction of developers being introduced to NUnit is "What? That's all I have to do?". To get started, visit this page on the NUnit website, and follow the steps in the first paragraph "Getting Started with NUnit".

When I began writing unit tests in early 2003, I wrote tests for existing code. If this code (e.g. a library) is already successfully in use, this can be pretty frustrating, because the most basic tests are all likely to succeed. My first tests where pretty coarse, testing too much at once - maybe because the trivial tests (e.g. create a class instance, set a property and test whether reading it has the expected result) seemed like a waste of time.

In the course of time I moved more towards "test driven development", i.e. writing tests along with the code, often even before the implementation is ready. Now, if I create a new project, I always add a test project to the solution. This way my code and the corresponding tests never run out of sync. If I make a breaking change, the solution won't compile - it's that easy.

If you take this approach (writing test very early), even testing the most basic stuff can be pretty rewarding:

  • Sometime typos or copy/paste mistakes are not caught by the compiler (e.g. when the property getter accesses a different member variable than the property setter) - one bug like this found by a unit test written in 5 Minutes can save you hours of debugging through a complete application.
  • It's a very good test for the usability e.g. of your API. If it turns out that even a simple task requires many lines of code, you definitely should re-design your API (which is less of a problem at that early stage of development).
  • The unit tests is some sort of documentation of how your code is used - don't underestimate how helpful this can be (by the way: I wrote a simple tool for generating examples for online documentation from unit tests).
  • Last but not least: I know that some of the unit-testing folks don't like debuggers, but fine-grained unit tests are very good entry points for single stepping through your code.

So... what about a New Year's Resolution to start writing unit tests?


  • I agree whole heartedly. Writing your tests firsts really makes you think about what you need from your classes and how they're going to be used.

    Recently I had to design a tricky class, while my first instincts where to get going with it straigh away I instead wrote the tests. Doing so made me realise that the implementation I had assumed I need wasn't quite right.

    Its difficult to explain but I think that if I had gone straight into coding the class I would have been down a few dead ends and had to backtrack a few times before I got it right. But by writing the tests actually coding the class was much more straightforward.

  • You should make sure you let everyone know that once they start they'll never go back. TDD is addictive :)

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