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Blog Archive

Thu, 03 Nov 2005

Defect Driven Test Creation

Defect Driven Testing is a great way to start accumulating testing coverage on a product that's already in the field. It's a pretty simple idea that lots of people are already using under different names.

The steps are simple.

  1. Find a bug (also called a defect) in your product. Okay, I know this never happens to ~you~, but other people in your shop can use this. ;)
  2. Write an automated test that exposes the bug. This test should fail with a message that points out the defect.
  3. Take the test that fails and then work on your code until the test no longer fails. You know the code is fixed when the test stops failing. If the test doesn't fail anymore but the bug isn't completely fixed, fix the test you have already or add another one. This step is a lot like Test Driven Development.
  4. Add the test to your Continuous Integration system so that it will be run every time the code changes. This will keep the defect from sneaking back into the product. When the defect does show up, laugh loudly and stomp it out again.

That's it. It's pretty simple stuff but very effective. What are the key points here?

First, write the tests for the areas of the code that need tests. Whether this code is under active development or is just intricate, you'll be adding tests directly on top of the code with known issues. It's possible that other areas of your code need automated tests more, but you can address those areas when you're actually fixing bugs in those areas.

Second, you'll be adding tests in familiar code areas. I say it's familiar because you've been tracking down bugs in the area. This means you don't have to go learn a package to write tests for it. You're already invovled. Take advantage of that.

Third, bugs generally come back to haunt you. Many developers keep multiple copies of the code on their machines. When they fix a bug in one tree, they don't always get the fix into the other trees. Then they commit code in the other trees along with your pesky defect. Instant bug regression. You can "innoculate" your code against regressions by testing in a Continuous Integration system.

Also, when you add one test, be sure to play a little test Jazz. Variations on a theme. You'll often find more than one bug in an area.

Try out Defect Driven Testing the next time you have to track down a bug and squash it. You can build a very effective test suite in a short amount of time.

btw, related blog entries are Types of Tests, A Short JUnit Tutorial, and JUnit is not a Unit Testing framework. Sorry for the Java bias. I plan on adding more dotNet resources as time allows, but the ideas do apply.



posted at: 20:10 | path: | permanent link to this entry

No Fluff Just Stuff was awesome!

I spoke in both Atlanta and Reston's NFJS software symposiums and had a great time. I think I had a better time meeting and getting to know the other speakers than presenting... but presenting was a blast too.

I'm trying to give you a flavor for the types of people you'll run into and get to talk with if you get a chance to attend a NFJS. So here's a quick list of a few of the people I got to spend a few minutes with over the last two weekends, in no particular order.

I'm just going to stop at this point. The post would go too long if I told you about getting to talk with Dave Thomas, Mark Richards, Floyd Marinescu, Paul Duvall, Ted Neward, and others. Let me just say that attending a NFJS symposium will give you a chance to mingle with some very smart people and potentially pick their brains about the future of our industry. I consider myself very fortunate to a part of the conference.

Btw, those of you who were kind enough to fill out evaluation forms for me in Atlanta and Reston, thank you. I made the cut and should be on the tour next year. I appreciate all your feedback and hope to incorporate your comments into next year's talks.

posted at: 17:51 | path: | permanent link to this entry