delegate_matcher.rb

# RSpec matcher to spec delegations.
# Forked from https://gist.github.com/ssimeonov/5942729 with fixes
# for arity + custom prefix.
#
# Usage:
#
#     describe Post do
#       it { should delegate(:name).to(:author).with_prefix } # post.author_name
#       it { should delegate(:name).to(:author).with_prefix(:any) } # post.any_name
#       it { should delegate(:month).to(:created_at) }
#       it { should delegate(:year).to(:created_at) }
#       it { should delegate(:something).to(:'@instance_var') }
#     end

RSpec::Matchers.define :delegate do |method|
  match do |delegator|
    @method = @prefix ? :"#{@prefix}_#{method}" : method
    @delegator = delegator

    if @to.to_s[0] == '@'
      # Delegation to an instance variable
      old_value = @delegator.instance_variable_get(@to)
      begin
        @delegator.instance_variable_set(@to, receiver_double(method))
        @delegator.send(@method) == :called
      ensure
        @delegator.instance_variable_set(@to, old_value)
      end
    elsif @delegator.respond_to?(@to, true)
      unless [0,-1].include?(@delegator.method(@to).arity)
        raise "#{@delegator}'s' #{@to} method does not have zero or -1 arity (it expects parameters)"
      end
      @delegator.stub(@to).and_return receiver_double(method)
      @delegator.send(@method) == :called
    else
      raise "#{@delegator} does not respond to #{@to}"
    end
  end

  description do
    "delegate :#{@method} to its #{@to}#{@prefix ? ' with prefix' : ''}"
  end

  failure_message_for_should do |text|
    "expected #{@delegator} to delegate :#{@method} to its #{@to}#{@prefix ? ' with prefix' : ''}"
  end

  failure_message_for_should_not do |text|
    "expected #{@delegator} not to delegate :#{@method} to its #{@to}#{@prefix ? ' with prefix' : ''}"
  end

  chain(:to) { |receiver| @to = receiver }
  chain(:with_prefix) { |prefix| @prefix = prefix || @to }

  def receiver_double(method)
    double('receiver').tap do |receiver|
      receiver.stub(method).and_return :called
    end
  end
end

@hrieke i suggest taking a look at @dwhelan's gem.

Unfortunately this gist is a fork of many before it so I can't give away full ownership of the code

Okay, I've gone and asked the others as well. I'll let you know if I hear back from any of them.
The problem is that even Declan Whelan's code has your code in it, which technically you, and those you forked from own. Toss in US copyright law, is enough to make this mountain boy curse in yiddish.

Any code of mine in this gist is covered by MIT license

Awesome. Thank you so much. I'll update the others with your note and hopefully they all do the same.

Henry, happy to help if I can. Is there anything specific you would like from me?

Hello Declan,
Thank you for your offer of assistance, but everyone that I have asked to assign a license to their code has (looking at you txus...).
Have a great summer, both of you.