I went through that . So basically there is nothing OOTB for 'Activity' rule. I was hoping if there is way to capture 'tracer run of an activity' , then we could implement a logic on top of it to calculate % coverage.
From Pega 7.4 onwards, a new feature Test Coverage has been introduced which reports, among other things, whether an activity rule has been executed or not but does not yet report the number of steps covered. Apart from this, one can download the tracer events log and use it for further processing but not available on clipboard of any thread.