Testing your code is one of the best things you can do for the quality of your app. For a project as large as YUI this can present a number of challenges. Reid Burke in his YUIConf presentation “Testing YUI Everywhere” talks about the issues he faces daily in keeping our CI system up and healthy. You’ll definitely find some great insights into how we test our code and get a glimpse of the work he’s been doing. You can find the previous YUIConf talk here, and watch all of them via YouTube.
You can find Reid’s slides on his own site.