How to develop and test the app for Raspberry Pi (mostly GPIO) without RaspberryPi?

I work on the application for Raspberry Pi, that is a radioclock. I write it in Ruby using PiPiper. What I want do achieve - I want to write it on my laptop, without constant testing of outputs and inputs on actual Raspberry Pi. I want to write some code, write tests and stub / mock / fake GPIO signals. What is the best way to achieve it?