Why Write Unit Tests?

Why Write Unit Tests?

I've made a small video to go with this post






Approval Tests have allowed us to focus on the parts of testing at a much higher level of abstraction. Things that had been too hard to see have become visible. The benefits of Automated Tests are one of the areas that we can now more clearly appreciate. There are 4 main areas programmers can benefit from using Automated Tests (Unit and otherwise)

1. Specifications
2. Feedback
3. Regression
4. Granularity

Let's talk about each of these.

First, there is Specifications. Everyone knows that good requirements help programmers to produce better software. Well, you can't do better than a running, failing unit test. This gives a clearly defined goal, and provides a executable document of the Users Intent. Focusing on this particular area, has led to the emergence of Behavior Driven Development (BDD).


Fast Feedback. After you know what you want to write, it's very helpful to know that you are fulfilling that requirement. Feedback allows you to know when you have made a mistake, or a wrong turn. Imagine you are driving to Disneyland and you miss your turn. When would you like to know that? Immediately afterwards? 10 minutes later? 6 hours later? Or only when you reach the east coast? Feedback from your test can tell you within seconds if you didn't code what you thought you did. Compare that to sending it to QA and getting a bug report back next week. Focusing on this particular area has led to Test Driven Development (TDD), and is what they are referring to when they speak of bouncing between the red & green bars.

Regression Testing is what most people actually think of when they talk about testing. This is all about maintaining & assuring the quality of the code (by which I mean, is the code working). Focusing on this aspect of testing brings about Acceptance Testing and products like Selenium & Fitness.

And finally Granularity. Imagine the following bug report: "The software has a bug." While this is sufficient to tell you whether or not you have bug free software, it's not at all useful in helping you to remove that bug. (If you've ever done a google code jam, this is exactly what the bug reports look like by the way.) It's nice to have some granularity pointing you to the problem. Something like "if you select user #6 and run a expense report for July 7th, line 15 says $34 when it should say $65". Now that's helpful! Again, TDD is really the area most focused on small granular tests, partly because granularity and feedback are highly related.

Hopefully, you will start to see these 4 features of testing as you continue to unit test. I don't want to place any sort of hierarchy of value on them right now, just point out that they are all valuable. Of course, if you are using approval tests, you'll see how they can aid each and every one of these categories!