rake yard:strict

Rakefile

  namespace :yard do
    desc "Generate YARD docs and fail unless every object (incl. private) is documented"
    task strict: :yard do
      require "open3"
      out, = Open3.capture2("yard", "stats", "--list-undoc", "--private", "--protected")
      puts out
      coverage = out[/([\d.]+)% documented/, 1]&.to_f
      abort "yard:strict could not parse coverage from `yard stats` output" if coverage.nil?
      abort "yard:strict failed: #{coverage}% documented (< 100%)" if coverage < 100.0
    end
  end
rescue LoadError
  # YARD is a development dependency; its tasks are simply unavailable without it.
end