thoughtbot--shoulda-matchers/lib/shoulda/matchers/active_record/accept_nested_attributes_for_matcher.rb

module Shoulda
  module Matchers
    module ActiveRecord
      # Ensures that the model can accept nested attributes for the specified
      # association.
      #
      # Options:
      # * <tt>allow_destroy</tt> - Whether or not to allow destroy
      # * <tt>limit</tt> - Max number of nested attributes
      # * <tt>update_only</tt> - Only allow updates
      #
      # Example:
      #   it { should accept_nested_attributes_for(:friends) }
      #   it { should accept_nested_attributes_for(:friends).
      #                 allow_destroy(true).
      #                 limit(4) }
      #   it { should accept_nested_attributes_for(:friends).
      #                 update_only(true) }
      #
      def accept_nested_attributes_for(name)
        AcceptNestedAttributesForMatcher.new(name)
      end

      class AcceptNestedAttributesForMatcher
        def initialize(name)
          @name = name
          @options = {}
        end

        def allow_destroy(allow_destroy)
          @options[:allow_destroy] = allow_destroy
          self
        end

        def limit(limit)
          @options[:limit] = limit
          self
        end

        def update_only(update_only)
          @options[:update_only] = update_only
          self
        end

        def matches?(subject)
          @subject = subject
          exists? &&
            allow_destroy_correct? &&
            limit_correct? &&
            update_only_correct?
        end

        def failure_message_for_should
          "Expected #{expectation} (#{@problem})"
        end

        def failure_message_for_should_not
          "Did not expect #{expectation}"
        end

        def description
          description = "accepts_nested_attributes_for :#{@name}"
          if @options.key?(:allow_destroy)
            description += " allow_destroy => #{@options[:allow_destroy]}"
          end
          if @options.key?(:limit)
            description += " limit => #{@options[:limit]}"
          end
          if @options.key?(:update_only)
            description += " update_only => #{@options[:update_only]}"
          end
          description
        end

        protected

        def exists?
          if config
            true
          else
            @problem = 'is not declared'
            false
          end
        end

        def allow_destroy_correct?
          failure_message = "#{should_or_should_not(@options[:allow_destroy])} allow destroy"
          verify_option_is_correct(:allow_destroy, failure_message)
        end

        def limit_correct?
          failure_message = "limit should be #{@options[:limit]}, got #{config[:limit]}"
          verify_option_is_correct(:limit, failure_message)
        end

        def update_only_correct?
          failure_message = "#{should_or_should_not(@options[:update_only])} be update only"
          verify_option_is_correct(:update_only, failure_message)
        end

        def verify_option_is_correct(option, failure_message)
          if @options.key?(option)
            if @options[option] == config[option]
              true
            else
              @problem = failure_message
              false
            end
          else
            true
          end
        end

        def config
          model_config[@name]
        end

        def model_config
          model_class.nested_attributes_options
        end

        def model_class
          @subject.class
        end

        def expectation
          "#{model_class.name} to accept nested attributes for #{@name}"
        end

        def should_or_should_not(value)
          if value
            'should'
          else
            'should not'
          end
        end
      end
    end
  end
end