Test caching for show_related_resource requests

Author: lgebhardt

test/test_helper.rb

@@ -592,8 +592,7 @@ def assert_cacheable_get(action, *args)
       end
 
       if mode == :all
-        # TODO Should also be caching :show_related_resource (non-plural) action
-        if [:index, :show, :show_related_resources].include?(action)
+        if [:index, :show, :show_related_resource, :show_related_resources].include?(action)
           if ar_resource_klass && response.status == 200 && json_response["data"].try(:size).try(:>, 0)
             assert_operator(
               cache_activity[:warmup][:total][:misses],