The above has a few online testing features (some better than others) and a few examples and tutorials.
Prob. easiest - CodeIgniter - it's very loose/forgiving/flexible - so that may be be bad/good.
Other good ones I've used to varying extents:
I really like Yii, but it's still a young framework, so not as well supported as the other two.
I've never used Zend as it looked a bit complicated to set up (server and all), but pros tend to rave about it.