Add a Responder to handle respond_with(resource)

test/test_helper.rb

@@ -15,6 +15,9 @@ require "active_model_serializers"
 require "active_support/json"
 require "test/unit"
 
+# Manually include RenderJsonOverride where needed
+ActiveModel::Serializer.use_default_render_json = true
+
 require 'rails'
 
 module TestHelper