Previously I mentioned the excellent Xcode Injection plugin from John Holdsworth allowing runtime code injection.
Here’s another great tool from John that comes in the form of a library called Xtrace that lets you see exactly what is happening with a class.
Xtrace allows you to easily log all method calls to a class or a particular class instance and return values sent.
Xtrace is easy to use you simply need to import the library (full details on the Github page) and run it with [classname xtrace] or [instancename xtrace].
There are also a number of other handy features such as the ability to filter out specific methods using a regular expression, and an example project is included.
You can find Xtrace on Github here.
A very nice library for tracking exactly what is happening to a class.