In this new post to his blog Chris Hartjes suggests a new way to judge frameworks - how easy they make it to write unit tests against them and their resulting applications.

As a project for work gets ready for an alpha release, I've managed to eliminate all the serious bugs and now have some time for what should've been part of the project from the beginning: writing tests. [...] Since I'm using Code Igniter instead of CakePHP for this project (did I mention that I inherited the project and couldn't switch?) I started looking into the culture of testing surrounding Code Igniter. It's weaker than a newborn baby.

He tried to find anything he could use to write tests against the CodeIgniter application and finding fooStack as an easy to use tool for the job. This was what made him wonder how other frameworks stack up in the "has good unit testing functionality" category. He briefly covers four of them - CodeIgniter, Zend Framework, CakePHP and Symfony.

So now when you start comparing frameworks to each other, I think it's important you also consider how much effort has gone into creating tests for the core functionality of that framework. A well tested framework should mean far less surprises when using it.