An RSpec2 matcher for ActiveModel errors.

have_error_on.rb

# Hey look, a matcher for RSpec2 that will check for an error on an ActiveModel attribute, given a I18n key and interpolation options.
#
# I feel like this should exist somewhere already, I am probably wrong though. 
#
# @foo.should have_error_on(:bar, :bar_is_too_baz, :quux => :corge)
#

module RSpec
  module Matchers
    class HaveErrorOn
  
      def initialize(attribute,key,options={})
        @attribute = attribute
        @key = key
        @options = options
      end
  
      def matches?(actual)
        @actual = actual
        @expected_message = @actual.errors.generate_message(@attribute, @key, @options)
      
        @actual.valid? # re-run validations
      
        @actual.errors[@attribute].include?(@expected_message)
      end
  
      def failure_message_for_should
        "expected #{@actual.inspect} to have error #{@key} on attribute #{@attribute}"
      end

      def failure_message_for_should_not
        "expected #{@actual.inspect} to not have error #{@key} on attribute #{@attribute}"
      end

      def description
        "have error #{@key} on attribute #{@attribute}"
      end
    
    end

    def have_error_on(attribute,key,options={})
      Matchers::HaveErrorOn.new(attribute,key,options)
    end

  end
end