handy rspec it_delegates matcher

delegates_matcher.rb

module RSpec::Example::DelegatesMatcher
  def it_delegates(*args)
    options = args.pop
    if options.is_a?(Hash)
      options.symbolize_keys!
      delegated_instance = options.fetch(:to) { raise 'You must provide a :to option to it_delegates' }
    else
      raise 'You must provide an options hash to it_delegates'
    end

    args.each do |method|
      describe method do
        it "delegates #{method} to #{delegated_instance}" do
          instance = stub(delegated_instance)
          subject.stub(delegated_instance) { instance }
          args = stub('Args')
          result = stub('Result')
          instance.should_receive(method).with(args) { result }
          eval("subject.#{method}(args)").should == result
        end
      end
    end
  end
end

some_spec.rb

class Some
  delegate :thing, :to => :otherthing

  def otherthing
    Class.new do
      def thing(man)
        man
      end
    end
  end
end

describe Some do
  it_delegates(:thing, :to => :otherthing)
end

spec_helper.rb

RSpec.configure do |config|
  config.extend(RSpec::Example::DelegatesMatcher)
end