Writing rake tasks, how do I interactively debug them in RubyMine?

I'm writing a Gem that contains Rake tasks. I want to set breakpoints and inspect the gem codebase during task execution. How can I do this in RubyMine?  I tried setting up a Rake debug config, but when I run it in the IDE I get the response "don't know how to build task 'taskname'"

This Gem is not consumed by other code, its tasks are commands I use from the command shell (os/x terminal window) to manage devops tasks.

So I don't have another codebase I can step into these tasks from...