validation_matcher.rb

module ValidationMatcher
    class BeValid
      def matches?(target)
        @target = target
        @target.valid?
      end
      def failure_message
        "expected #{@target} to be valid, but:\n" +
        @target.errors.map { |a, m| "- #{a.humanize} #{m} (#{a}: #{@target[a].inspect})" }.join("\n")
      end
      def negative_failure_message
        "expected #{@target.inspect} not to be valid, but it was."
      end
    end

    def be_valid
      BeValid.new
    end
end