Allow fast checkout without re-accepting old terms

We did that for the shop's terms already and now do it for the platform
terms as well.

spec/features/consumer/shopping/checkout_spec.rb

@@ -200,6 +200,32 @@ feature "As a consumer I want to check out my cart", js: true do
         uncheck "Terms of service"
         expect(page).to have_button("Place order now", disabled: true)
       end
+
+      context "when the terms have been accepted in the past" do
+        before do
+          TermsOfServiceFile.create!(
+            attachment: File.open(Rails.root.join("public/Terms-of-service.pdf")),
+            updated_at: 1.day.ago,
+          )
+          customer = create(:customer, enterprise: order.distributor, user: user)
+          customer.update(terms_and_conditions_accepted_at: Time.zone.now)
+        end
+
+        it "remembers the acceptance" do
+          visit checkout_path
+
+          within "#checkout_form" do
+            expect(page).to have_link("Terms of service")
+            expect(page).to have_button("Place order now", disabled: false)
+          end
+
+          uncheck "Terms of service"
+          expect(page).to have_button("Place order now", disabled: true)
+
+          check "Terms of service"
+          expect(page).to have_button("Place order now", disabled: false)
+        end
+      end
     end
 
     context "when the seller's terms and the platform's terms have to be accepted" do

spec/models/terms_of_service_file_spec.rb

@@ -33,4 +33,22 @@ describe TermsOfServiceFile do
       expect(subject).to match /^\/system\/terms_of_service_files\/attachments.*Terms-of-service\.pdf\?\d+$/
     end
   end
+
+  describe ".updated_at" do
+    let(:subject) { TermsOfServiceFile.updated_at }
+
+    it "gives the most conservative time if not known" do
+      Timecop.freeze do
+        expect(subject).to eq Time.zone.now
+      end
+    end
+
+    it "returns the time when the terms were last updated" do
+      update_time = 1.day.ago
+      file = TermsOfServiceFile.create!(attachment: pdf, updated_at: update_time)
+
+      # The database isn't as precise as Ruby's time and rounds.
+      expect(subject).to be_within(0.001).of(update_time)
+    end
+  end
 end