This class returns a set of *.rb files which are not present in a SimpleCov resultset

coverage_checker.rb

# This class returns a set of *.rb files which are not present in a SimpleCov resultset
#
require 'json'
require 'set'

class CoverageChecker
  def missed_files(dir = 'app')
    uncovered_files(dir)
  end

  private

  def covered_files
    @covered_files ||= resultset.inject(Set.new) do |files, (key, val)|
      files += val['coverage'].keys.map{ |file| file.gsub(Dir.pwd + '/', '') }
      files
    end
  end

  def uncovered_files(path)
    if File.file?(path) &&
       File.extname(path) == '.rb' &&
       !covered_files.include?(path)
      [path]
    elsif File.directory?(path)
      Dir["#{path}/*"].map do |subpath|
        uncovered_files(subpath)
      end.flatten.compact
    end
  end

  def resultset
    JSON.parse File.read(simplecov_resultset_path)
  end

  def simplecov_resultset_path
    'coverage/.resultset.json'
  end
end

Gem released at https://github.com/gtd/simplecov_checker