What Are the Code Coverage Metrics for Ruby on Rails?

At FastRuby.io we are constantly looking at code coverage metrics for Ruby on Rails applications. It's a key indicator for us. We even use that information to decide whether we work on a Rails upgrade project or not.So, I was interested in seeing code coverage metrics for the Ruby on Rails framework. I couldn't find any information about this online, so I decided to generate a few reports for each component.This is an article about my process and my findings.