shoulda-matchers attempting to create errors container

example_failing_spec.rb

require 'spec_helper'

class FakeOrder
  include ActiveModel::Validations
  attr_accessor :site_ids, :user_id
  validate :validate_at_least_one_site_chosen
  validates_presence_of :user_id

  def validate_at_least_one_site_chosen
    errors.add(:site, "please choose at least one site")
  end
end

puts "Validating FakeOrder"
f = FakeOrder.new
f.valid?
puts "--> f.errors.messages: #{f.errors.messages}"

describe FakeOrder do
  describe 'validations' do
    it { should validate_presence_of :user_id }
  end
end

output.txt

$ be rspec spec/models/fake_order_spec.rb

Validating FakeOrder
--> f.errors.messages:
:site => please choose at least one site

FakeOrder
  validations
    should require user_id to be set (FAILED - 1)

Failures:

  1) FakeOrder validations
     Failure/Error: it { should validate_presence_of :user_id }
     NoMethodError:
       undefined method `site' for #<FakeOrder:0x1090b88f8>
     # ./spec/models/fake_order_spec.rb:21

Finished in 0.99055 seconds
1 example, 1 failure

Failed examples:

rspec ./spec/models/fake_order_spec.rb:21 # FakeOrder validations