Add tests to ensure compute amount doesn't persist

We want to make sure we don't persist anything when computing amounts
becuase that will cause issues with the in-memory order updater.

Author: AlistairNorman

legacy_promotions/spec/models/spree/promotion/actions/create_adjustment_spec.rb

@@ -126,4 +126,42 @@
       is_expected.to eq(Spree::Config.promotions.calculators[described_class.to_s])
     }
   end
+
+  describe "#compute_amount" do
+    subject { action.compute_amount(order) }
+
+    before do
+      promotion.promotion_actions = [action]
+      action.calculator = Spree::Calculator::FlatRate.new(preferred_amount:)
+    end
+
+    let(:preferred_amount) { 50 }
+
+    context "when the adjustable is actionable" do
+      it "calls compute on the calculator" do
+        expect(action.calculator).to receive(:compute).with(order).and_call_original
+        subject
+      end
+
+      it "doesn't persist anything to the database" do
+        allow(action.calculator).to receive(:compute).with(order).and_call_original
+
+        expect {
+          subject
+        }.not_to make_database_queries(manipulative: true)
+      end
+
+      context "calculator returns amount greater than order total" do
+        let(:preferred_amount) { 300 }
+
+        before do
+          allow(order).to receive_messages(item_total: 50, ship_total: 50)
+        end
+
+        it "does not exceed it" do
+          expect(subject).to eql(-100)
+        end
+      end
+    end
+  end
 end

legacy_promotions/spec/models/spree/promotion/actions/create_item_adjustments_spec.rb

@@ -92,13 +92,23 @@ module Spree
       end
     end
 
-    context "#compute_amount" do
+    describe "#compute_amount" do
+      subject { action.compute_amount(line_item) }
+
       before { promotion.promotion_actions = [action] }
 
       context "when the adjustable is actionable" do
         it "calls compute on the calculator" do
           expect(action.calculator).to receive(:compute).with(line_item).and_call_original
-          action.compute_amount(line_item)
+          subject
+        end
+
+        it "doesn't persist anything to the database" do
+          allow(action.calculator).to receive(:compute).with(line_item).and_call_original
+
+          expect {
+            subject
+          }.not_to make_database_queries(manipulative: true)
         end
 
         context "calculator returns amount greater than item total" do
@@ -108,7 +118,7 @@ module Spree
           end
 
           it "does not exceed it" do
-            expect(action.compute_amount(line_item)).to eql(-100)
+            expect(subject).to eql(-100)
           end
         end
       end

legacy_promotions/spec/rails_helper.rb

@@ -27,6 +27,7 @@
 require 'rspec/rails'
 require 'rspec-activemodel-mocks'
 require 'database_cleaner'
+require 'db-query-matchers'
 
 Dir["./spec/support/**/*.rb"].sort.each { |f| require f }
 

promotions/spec/models/solidus_promotions/benefit_spec.rb

@@ -122,6 +122,25 @@ def compute_line_item(_line_item, _options) = 1
     end
   end
 
+  describe "#compute_amount" do
+    subject { benefit.compute_amount(discountable) }
+
+    let(:variant) { create(:variant) }
+    let(:order) { create(:order) }
+    let(:discountable) { Spree::LineItem.new(order: order, variant: variant, price: 10, quantity: 1) }
+    let(:promotion) { SolidusPromotions::Promotion.new(customer_label: "20 Perzent off") }
+    let(:calculator) { SolidusPromotions::Calculators::Percent.new(preferred_percent: 20) }
+    let(:benefit) { described_class.new(promotion: promotion, calculator: calculator) }
+
+    it "doesn't save anything to the database" do
+      discountable
+
+      expect {
+        subject
+      }.not_to make_database_queries(manipulative: true)
+    end
+  end
+
   describe ".original_promotion_action" do
     let(:spree_promotion) { create :promotion, :with_adjustable_action }
     let(:spree_promotion_action) { spree_promotion.actions.first }

promotions/spec/models/solidus_promotions/benefits/adjust_line_item_quantity_groups_spec.rb

@@ -50,6 +50,14 @@
         context "and an item with a quantity of 3" do
           let(:quantity) { 3 }
           it { is_expected.to eq(-10) }
+
+          it "doesn't save anything to the database" do
+            line_item
+
+            expect {
+              subject
+            }.not_to make_database_queries(manipulative: true)
+          end
         end
 
         context "and an item with a quantity of 4" do