Enable oj to AM for fair benchmark test

Author: minsikzzang

spec/spec_helper.rb

@@ -3,6 +3,7 @@
 require 'multi_json'
 require 'byebug'
 require 'active_model_serializers'
+require 'oj'
 
 Dir[File.dirname(__FILE__) + '/shared/contexts/*.rb'].each {|file| require file }
 
@@ -13,6 +14,7 @@
   end
 end
 
+Oj.optimize_rails
 ActiveModel::Serializer.config.adapter = :json_api
 ActiveModel::Serializer.config.key_transform = :underscore
 ActiveModelSerializers.logger = ActiveSupport::TaggedLogging.new(ActiveSupport::Logger.new('/dev/null'))