On the Delicious Brains site there's a tutorial posted that shows you how to use XDebug for advanced PHP debugging versus some of the usual practices of var_dump or print_r-ing your way through your testing.

You could just debug your PHP code using functions such as error_log, print, and var_dump, (and to be honest we’ve all done it, a lot!), but sometimes they just aren’t enough, and can actually slow you down while developing.

There must be a better way, surely?! Enter Xdebug, the rather awesome debugging and profiling tool for PHP.

In this post, I’ll take you through why Xdebug is amazing, getting it setup, how to use it, get the most out of it it, and some neat advanced uses all to make your life easier.

He starts with some background on his previous debugging practices and how discovering XDebug revolutionized his workflow. He then talks about breakpoints for debugging and what he calls "debug driven development". The article then walks you through the installation process and the integration with IDEs, specifically PHPStorm. The rest of the post shows examples of how to use XDebug along with breakpoints and IDE features to get more information about the current application state and where things are failing. He also includes sections about using XDebug for profiling and performing remote debugging via an SSH tunnel.