Refactor voucher: 2 FlatRate voucher

app/models/vouchers/flat_rate.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: false
+
+module Vouchers
+  class FlatRate < Voucher
+    validates :amount,
+              presence: true,
+              numericality: { greater_than: 0 }
+
+    def display_value
+      Spree::Money.new(amount)
+    end
+
+    # We limit adjustment to the maximum amount needed to cover the order, ie if the voucher
+    # covers more than the order.total we only need to create an adjustment covering the order.total
+    def compute_amount(order)
+      -amount.clamp(0, order.pre_discount_total)
+    end
+  end
+end

spec/factories/voucher_factory.rb

@@ -6,9 +6,7 @@ FactoryBot.define do
     amount { 10 }
   end
 
-  factory :voucher_percentage, class: Voucher do
-    enterprise { build(:distributor_enterprise) }
-    voucher_type { Voucher::PERCENTAGE_RATE }
-    amount { rand(1..100) }
+  factory :voucher_flat_rate, parent: :voucher, class: Vouchers::FlatRate do
+    amount { 15 }
   end
 end

spec/models/vouchers/flat_rate_spec.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Vouchers::FlatRate do
+  let(:enterprise) { build(:enterprise) }
+
+  describe 'validations' do
+    subject { build(:voucher_flat_rate, code: 'new_code', enterprise: enterprise) }
+
+    it { is_expected.to validate_presence_of(:amount) }
+    it { is_expected.to validate_numericality_of(:amount).is_greater_than(0) }
+  end
+
+  describe '#compute_amount' do
+    let(:order) { create(:order_with_totals) }
+
+    context 'when order total is more than the voucher' do
+      subject { create(:voucher_flat_rate, code: 'new_code', enterprise: enterprise, amount: 5) }
+
+      it 'uses the voucher total' do
+        expect(subject.compute_amount(order).to_f).to eq(-5)
+      end
+    end
+
+    context 'when order total is less than the voucher' do
+      subject { create(:voucher_flat_rate, code: 'new_code', enterprise: enterprise, amount: 20) }
+
+      it 'matches the order total' do
+        expect(subject.compute_amount(order).to_f).to eq(-10)
+      end
+    end
+  end
+end