rspec_delegate_matcher.rb

# RSpec matcher to spec delegations.
#
# Usage:
#
#     describe Post do
#       it 'delegates name to Author' do
#           expect subject.to delegate(:name).to(:author).with_prefix # post.author_name
#       end
#       it 'delegates month to creation date' do
#           expect subject.to delegate(:month).to :created_at
#        end
#       it { delegates(:year).to :created_at }
#     end
#
#     describe Toolbox
#       it { delegates(:api_endpoint).to Application::Config }
#     end

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

    unless delegator.respond_to? @method
      fail "#{delegator} does not respond to #{@to}!"
    end

    @target_name = "#{@to}#{@prefix ? ' with prefix' : ''}"

    receiver = @to.is_a?(Symbol) ? double(:receiver) : @to

    expect(receiver).to receive(method) { :called }

    if @to.is_a? Symbol
      expect(delegator).to receive(@to) { receiver }
    end

    delegator.send(@method) == :called
  end

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

  description do |actual|
    "#{actual} delegates :#{@method} to #{@target}"
  end

  failure_message do |actual|
    "expected #{actual} to delegate :#{@method} to #{@target}"
  end

  failure_message_when_negated do |actual|
    "expected #{actual} not to delegate :#{@method} to #{@target}"
  end
end