RSpec matcher for delegations

delegate_matcher.rb

# RSpec matcher to spec delegations.
#
# Usage:
#
#     describe Post do
#       it { should delegate(:name).to(:author).with_prefix } # post.author_name
#       it { should delegate(:month).to(:created_at) }
#       it { should delegate(:year).to(:created_at) }
#     end

RSpec::Matchers.define :delegate do |method|
  match do |delegator|
    @method = @prefix ? :"#{@to}_#{method}" : method
    @delegator = delegator
    begin
      @delegator.send(@to)
    rescue NoMethodError
      raise "#{@delegator} does not respond to #{@to}!" 
    end
    @delegator.stub(@to).and_return double('receiver')
    @delegator.send(@to).stub(method).and_return :called
    @delegator.send(@method) == :called
  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 = true }

end

Been looking for something like this, awesome work!

However, I get this error when I try to run this matcher:
it { should delegate(:name).to(:profile)}
error:
id is required for non-singleton resources

any idea what's going?

I'm afraid it has nothing to do with the delegator... Could you provide a full backtrace and maybe also the code for your model?

Exactly what I needed – thanks! -j

Thanks!

Cool thanks!

Thanks!

Awesome! Very useful.

You should try to get this into Shoulda!

This is cool but there are three small problems with this implementation:

1. It does not work in the case of delegating to instance variables, e.g., delegate :foo, to: :'@my_var'
2. Validating that the delegation target exists by using @delegator.send(@to) is an unexpected behavior from the standpoint of the user of the matcher. If there are any side effects from that call, the test outcome could be affected.
3. The rescue block won't catch arity-related errors.

All three issues are fixed in my fork: https://gist.github.com/ssimeonov/5942729

This fails if the method is a setter with error:

 Failure/Error: it{ should delegate(:name=).to(:sku_description)}

My fork has updated this gist to RSpec 3.3 version: https://gist.github.com/bparanj/4579700adca0b64e7ca0

Hahah! @txus ! Te veo hasta en la sopa :).

Hello,

Do you have a license that you would like to release this code under?
I spoke with Alec Winograd about his fork-of-Simeon's-fork (yep, 2 down), he's added an MIT License to his modifications.
I have also asked Simeon if he'd like to add a license to his modification, but it would be absolutely wonderful if you could assign a license to your code. [Edit] Simeon Simeonov has replied, and selected the MIT License for his modifications as well. [/Edit]

Thank you, hope all is well.

I'm using this for now but thanks for the original work 👏 ❤️

➡️ https://gist.github.com/purp/fe5f79e878b609560724d6b03242a5df