Rspec tests & helpers for ActiveModel::Serializers

customer_serializer.rb

# app/serializers/customer_serializer_spec.rb

class CustomerSerializer < ActiveModel::Serializer
  attributes :customer_number, :email, :username

  def customer_number
    object.account_number
  end

  def merchant_id
    object.username.first(20)
  end
end

customer_serializer_spec.rb

# spec/serializers/customer_serializer_spec.rb

require 'spec_helper'

describe CustomerSerializer do
  let(:object) do
    build_serializable(
      :account_number => "ACT123",
      :username => "newuser",
      :email => "email@service.com",
    )
  end

  subject { serialize(object) }

  it { should include(:customer_number => "ACT123") }
  it { should include(:username => "newuser") }
  it { should include(:email => "email@service.com") }
end

serializer_example_group.rb

# spec/support/serializer_example_group.rb

module SerializerExampleGroup
  extend ActiveSupport::Concern

  included do
    metadata[:type] = :serializer

    let(:serializable_class) do
      Class.new(OpenStruct) do
        include ActiveModel::Serialization
      end
    end

    def build_serializable(attributes={})
      serializable_class.new(attributes).tap do |obj|
        obj.stub(:read_attribute_for_serialization) { |name| attributes[name] }
      end
    end

    def serialize(object)
      described_class.new(object).serializable_hash.with_indifferent_access
    end
  end

  RSpec.configure do |config|
    config.include self,
      :type => :serializer,
      :example_group => { :file_path => %r(spec/serializers) }
  end
end

i get a NoMethod error for obj.stub on line 17 of serializer_example_group.rb