One big selling point for CakePHP is that its test framework is Simpletest, while ZF uses PHPUnit. The difference between these two is that simpletest has better mock object support.
This is important if you test first, then write code--which you really should try! it's liberating--because your controller frequently interacts with model (database) and view, so it's nice to know, by using a mock database/view, that your controller is doing exactly what it should. In other words, you have to have the mocks in order to fully test (i.e., define by means of tests) the controller's API.