SimpleCov

https://github.com/simplecov-ruby/simplecov

Ruby code coverage

[test|spec]_helper.rb

require 'simplecov'
SimpleCov.start do
  enable_coverage :branch
  add_filter '/app/admin/' # example: config for an admin UI that is just declaration
  add_filter '/config/'
  add_filter '/test/'
end

Run tests, then view coverage/index.html in browser