errors_matcher.rb

module Spec
  module Matchers
      
    RSpec::Matchers.define :have_errors_on do |field|
      chain :with_message do |message|
        @message = message
      end

      match do |model|
        model.valid?
        @has_error = has_error?(model, field)

        if @message
          @has_error && model.errors[field].include?(@message)
        else
          @has_error
        end
      end

      failure_message_for_should do |model|
        msg = "#{model.class} should have an error on field #{field.inspect}"

        if @has_error && @message
          msg << " with a message #{@message.inspect}"
          msg << " while it is #{model.errors[field].inspect}"
        end

        msg
      end

      failure_message_for_should_not do |model|
        "#{model.class} should not have an error on field #{field.inspect}"
      end

      description do
          
      end

      def has_error?(model, field)
        !model.errors[field].blank?
      end
    end

  end
end

user_spec.rb

require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')

describe User do
  describe "validation of " do
    subject { Factory.build(:invalid_user) }

    describe "email" do
      describe "when has less then 6 chars" do
        before(:each) { subject.email = 'f@b' }

        it { should have_errors_on(:email).with_message("Email must be between 6 and 64 characters long") }
      end

      describe "when has more then 64 chars" do
        before(:each) { subject.email = 'this.is.a.very.long.email.that.has.more.then.64.ch@rs.for.sure.com' }

        it { should have_errors_on(:email).with_message("Email must be between 6 and 64 characters long") }
      end

      describe "when has more then 6 and less then 64 chars" do
        before(:each) { subject.email = '[email protected]' }

        it { should_not have_errors_on(:email).with_message("Email must be between 6 and 64 characters long") }
      end
    end

    describe "first_name" do
      it { should have_errors_on(:first_name).with_message("First name must be between 3 and 50 characters long") }
    end

    describe "last_name" do
      it { should have_errors_on(:last_name).with_message("Last name must be between 3 and 50 characters long") }
    end

    describe "degree" do
      it { should have_errors_on(:degree).with_message("Degree is not included in the list") }
    end

    describe "password" do
      it { should have_errors_on(:password).with_message("Password must be between 6 and 20 characters long") }
    end
  end

  describe "default state" do
    before :all do
      @user = User.new
    end

    it "sets degree to mgr" do
      @user.degree.should eql('mgr')
    end
  end
end