gistfile1.txt

class PrecatoryParcel < Compras::Model
  attr_accessible :expiration_date, :value, :situation, :payment_date
  attr_accessible :amount_paid, :observation

  has_enumeration_for :situation, :with => PrecatoryParcelSituation

  belongs_to :precatory

  delegate :pledges, :to => :precatory, :prefix => true, :allow_nil => true

  validates :expiration_date, :value, :situation, :presence => true

  before_destroy :check_destroy

  def check_destroy
    if precatory_pledges.any?
      errors.add(:base, :cannot_be_changed_if_precatory_have_pledge)
	  end
	end
end




# encoding: utf-8
require 'model_helper'
require 'app/models/precatory_parcel'
require 'app/enumerations/precatory_parcel_situation'

describe PrecatoryParcel do
  it { should validate_presence_of :expiration_date }
  it { should validate_presence_of :value }
  it { should validate_presence_of :situation }

  it { should belong_to :precatory }

  context "destroy precatory_parcel" do
    before do
      subject.expiration_date = Date.new(2013, 01, 31)
      subject.value = 100
      subject.situation = PrecatoryParcelSituation::PAID
      subject.stub(:precatory).and_return(double("Precatorio").stub(:pledges).and_return(double("Emprenho"), :any? => true))
    end

    it "when precatory has pledge" do
      subject.destroy

      expect(subject.errors[:base]).to include 'não pode ser alterada. Este Precatório já possui Empenho'
    end
  end
end

faz assim:

Caso inválido:

subject.stub(:precatory_pledges => [])

Caso válido:

subject.stub(:precatory_pledges => [double])

Não esquece de retornar false depois de incluir o erro, senão ele vai excluir o registro do mesmo jeito.