In this new post to DZone.com Giorgio Sironi looks at a method for "recording" the request and response information for an application that might be lacking in documentation using PHP's output buffering.

So you've got this big ball of code. You don't even know how to call all of these scripts, but the code is in production and works just fine (until you have to change even a single line). How to define some characterization tests that describe how the .php scripts work now? [...] If tests do not exist, we do not know if they expect GET or POST requests, which parameters they contain, and above all what their response should be in correct and error cases. Even if all the links and calling code are under your control, it may be faster to go for the recording approach. If other applications and machines call your .php files, it is your only choice.

He suggests using ob_start and the output buffering methods to handle the recording as it lets us define a callback (or in his case, a recording object). He includes an abstract version of it, showing how to implement a "Tape" class and a "record" method to handle the data and push it into a log or some other recording mechanism.