SimpleCov provides a baseline rails setting

spec/rails_helper.rb

@@ -2,9 +2,7 @@
 
 # This file is copied to spec/ when you run 'rails generate rspec:install'
 require 'simplecov'
-SimpleCov.start do
-  add_filter %r{^/spec/}
-end
+SimpleCov.start('rails')
 
 require 'spec_helper'
 require 'capybara_helper'