The SitePoint PHP blog has a new tutorial posted by i>Miguel Ibarra Romero showing how to use the PsySH tool to do some interactive debugging of your PHP applications via both the command line and a web frontend.
He walks you through the install via Composer and some of the basic commands and syntax for executing PHP code inside its shell. Command line testing is good, but debugging full applications is a bit more difficult. He shows how to integrate the tool into a sample application that calls PsySH via a "debug" call and output via a set of "window" objects. He also includes a bit close to the end about debugging with unit tests, executing them from inside the shell as well.