Sometimes I come across a way of putting something that it is pithy good, not Hallmark trite, but an impactful and concise way of clarifying a previously obscure concept. A recent one of these happy occurrences was when I was reading the excellent Art of Unit Testing by Roy Osherove.

After going through the basics of why youd want to test code and how to do it, Roy confronts a frequent objection to having unit tests, that it ends up changing how you design your components:

When we write unit tests for our code, we are adding another end user (the test) to the object model. That end user is just as important as the original one, but it has different goals when using the model.  The test has specific requirements from the object model that seem to defy the basic logic behind a couple of object-oriented principles, mainly encapsulation. [emphasis added by me]

When I read this, something clicked for me. I used to find it persuasive that because unit tests caused you to change your design they were more disruptive than they were worth. The counter argument I heard is that the disruption was OK, because testable design was just obviously better. That argument was not convincing as it seemed like delusional arrogance to suggest that any one of type of design was just inherently better for the particular applications I was building.

What was missing was that I was not thinking of unit tests as an additional and equal end user to my design. If I accepted that proposition, than it was indeed obvious that a testable design was better because now all users of my component would be satisfied.

Have I accepted that proposition? Id phrase it slightly different. I find more and more that having unit tests helps me write better, less buggy code before it gets to production or QA. As I write more unit tests, it gets easier to see how to create testable components, so I dont feel like its taking me as much extra time up front. I pick and choose components that seem most likely to benefit from automated tests and it is working out nicely.

If you already implement Test Driven Development, this whole post was probably a waste of your time <g> If you hate the idea of unit tests, well, probably not a great value prop for you either. However, if you are somewhere in between, at least take a minute and check out a sample chapter from Roys book at: http://www.manning.com/osherove/.

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