Example presenter

estimate_presenter.rb

class EstimatePresenter < SimpleDelegator
  def self.from_estimate_list(*estimates)
    estimates.flatten.map { |estimate| EstimatePresenter.new(estimate) }
  end
  
  def initialize(estimate)
    super
  end
  
  def insurance?
    type == "insurance"
  end
  
  def insurance_coverage
    return unless insurance?
    items.sum(&:insurance_rebate_value)
  end

  def gap_payment
    return private_value unless insurance?
    private_value - insurance_coverage
  end
end

Spec snippet

describe EstimatePresenter do

  let(:estimate) { instance_double(Estimate, type: "insurance") }
  let(:presenter) { EstimatePresenter.new(estimate) }

  describe '.insurance?' do
    it 'is an insurance type' do
      allow(estimate).to receive(:type).and_return('insurance')
      expect(presenter.insurance?).to be_true
    end
    it 'isnt an insurance type' do
      allow(estimate).to receive(:type).and_return('ponzy')
      expect(presenter.insurance?).to be_false
    end
  end
end

Of course 'insurance' is magic word ;)

Estimate::INSURANCE