improve test setup

spec/rails_helper.rb

@@ -62,3 +62,10 @@ RSpec.configure do |config|
   # arbitrary gems may also be filtered via:
   # config.filter_gems_from_backtrace("gem name")
 end
+
+Shoulda::Matchers.configure do |config|
+  config.integrate do |with|
+    with.test_framework :rspec
+    with.library :rails
+  end
+end