Test Driven Development

I've read a lot for and a lot against Test Driven Development (TDD) but I don't every remember something TDD has really helped me with. If you write a test then write the code which makes the test pass the end result is a piece of code which demonstrates how the application code works. I have used a number of open source applications and like every library/framework/application I have used the documentation ends up being way out of date. But if you are writing tests for all the features you add (before or after you write the code) you are essentially creating examples of how to use the library/framework/application. So even with the documentation falling out of date, so long as the code has a good base of unit tests, you can figure out how it works. I find this helpful in multiple ways. When I'm automating I tend to use tools like Selenium. Whenever I need to use a new feature of Selenium I can look at the documentation but ultimate, the unit tests for the framework tell me how it actually behaves. Additionally, the applications I am testing are written by people who understand TDD and have a good set of unit tests for each application. So I find it easy to under how new features are implemented by looking at the unit test for the application I am testing. For example, Selenium has a TakesScreenshot class. The source for it would be found at:

https://code.google.com/p/selenium/source/browse/java/client/src/org/openqa/selenium/TakesScreenshot.java

So if I want to see the tests for it, change 'src' to 'test' and change 'TakesScreenshot.java' to 'TakesScreenshotTest.java' for a full URL of:

https://code.google.com/p/selenium/source/browse/java/client/test/org/openqa/selenium/TakesScreenshotTest.java

When I look at this latter file I see many examples of how to use the TakesScreenshot class.