Example: custom rspec-mocks argument matcher

array_matching.rb

module ArrayMatching
  class ArrayMatching
    def initialize(array)
      @array = array
    end

    def ==(other_array)
      Set.new(@array) == Set.new(other_array)
    end

    def inspect
      "an array with elements #{@array.inspect}"
    end
  end

  # Matches arguments that contain the same elements as the given Array
  def array_matching(elements)
    ArrayMatching.new(elements)
  end
end

RSpec.configure do |config|
  config.include ArrayMatching
end

Usage:

updater.should_receive(:process).with(array_matching(operations))

I can no find any RSpec documentation about achieving the above example. Is there a link with more info you could provide?