Why is JBuilder not returning a response body in JSON when testing RSPEC

When testing a JSON response from an RSPEC controller test using DHH's JBuilder, my response.body is always "{}". It works fine in development/production modes AND when I use the to_json method instead of jbuilder, I get proper JSON in my response.body. Anyone have a clue as to why my response.body would always be "{}" when testing? ----- Debugger it "should return the cart items via JSON", :focus

[isseium]

はじめて jbuilder 使ったのはいいものの rspec が通らなくてハマってた．spec_helper に設定が必要だったみたい.