In this new post on ThinkingPHP.org, Felix Geisendorfer talks about some of the development work that he's been doing regarding CakePHP:

My first idea was to do unit testing on Controllers. I made a little comment about it here and uploaded some of my experimental code for that. In the beginning it looked very promising. I was able to mock Models & Components and add them to the Controller. But the deeper I got into it, the more I realized: Unit Testing with Controllers is insane

To back it up he points out some of the hurdles he had to work with and includes some of the code he used to test the Controllers he had made inside of CakePHP.