Inner classes to implement SRP in ruby

statistics.rb

class Statistics

  def initialize
    @configuration = Configuration.new(self)
  end

  delegate :for_caller,
           :rtp_errors,
           to: :@configuration

  class Configuration
    attr_accessor :test_campaign, :names

    def initialize(statistics)
      @statistics = statistics
    end

    def for_caller
      @sip_call_type = CallerSipCall.name
      @statistics
    end

    def rtp_errors
      @stats_type = "rtp_errors"
      @names = %w( late_packets lost_packets non_conforming_packets abandoned_packets )
      @statistics
    end

    def valid?
      @test_campaign.present? &&
              @sip_call_type.present? &&
              @stats_type.present?
    end
  end

  class Finder
    # ...
  end

  class ValueObject
    # ...
  end

end

statistics_spec.rb

# encoding: utf-8
require 'spec_helper'

describe Statistics do

  describe Statistics::Configuration do

    before :each do
      @statistics = Statistics.new
      @configuration = Statistics::Configuration.new(@statistics)
    end

    it "test campaign must be set" do
      @configuration.for_caller
      @configuration.rtp_errors

      expect(@configuration).not_to be_valid
    end

    it "caller or callee must be set" do
      @configuration.test_campaign = @test_campaign
      @configuration.rtp_errors

      expect(@configuration).not_to be_valid
    end

    it "stats type must be set" do
      @configuration.test_campaign = @test_campaign
      @configuration.for_caller

      expect(@configuration).not_to be_valid
    end

    it "is valid if the 3 previous parameters are set" do
      @configuration.test_campaign = stub_model(TestCampaign)
      @configuration.for_caller
      @configuration.rtp_errors

      expect(@configuration).to be_valid
    end

    it "choosing a stats type sets the list of stats which will be calculated" do
      @configuration.rtp_errors
      expect(@configuration.names).
              to eq(%w( late_packets lost_packets non_conforming_packets abandoned_packets))
    end

  end
end