Unit testing

I'm struggling to get unit testing to work.

Yii claims to have been built on top of PHPUnit, the base class CWebTestCase (/framework/test/CWebTestCase.php) contains an include of PHPUnit:

require_once('PHPUnit/Extensions/SeleniumTestCase.php');

But this file does not exists anywhere in the framework. I'm now trying to download and install PHPUnit manually, and putting it in the project under the vendors folder, but I'm not sure if this is the way to go, because I have to either change core files OR avoid Yii's test classes.

What's the best way to make PHPUnit work?