Selenium is a testing tool primarily used to record and playback scripts for web applicaiton. Your web application could have been developed in java, .Net, Perl, etc and even PEGA , and running in any standard browsers. Selenium would take care of this. Having said this, you do not have to do anyting special with Selenium in order to test Pega web applicaitons. Just follow the instrucitons given in the Selenium guide on how to record , playback and test any web application.