Add test coverage for handling zero priced orders

spec/controllers/split_checkout_controller_spec.rb

@@ -212,6 +212,26 @@
         end
       end
 
+      context "with a zero-priced order" do
+        let(:params) do
+          { step: "payment", order: { payments_attributes: [{ amount: 0 }] } }
+        end
+
+        before do
+          order.line_items.first.update(price: 0)
+          order.update_totals_and_states
+        end
+
+        it "allows proceeding to confirmation" do
+          put :update, params: params
+
+          expect(response).to redirect_to checkout_step_path(:summary)
+          expect(order.reload.state).to eq "confirmation"
+          expect(order.payments.count).to eq 1
+          expect(order.payments.first.amount).to eq 0
+        end
+      end
+
       context "with a saved credit card" do
         let!(:saved_card) { create(:stored_credit_card, user: user) }
         let(:checkout_params) do

spec/models/spree/order/payment_spec.rb

@@ -50,5 +50,22 @@ module Spree
 
       order.process_payments!
     end
+
+    context "with a zero-priced order" do
+      let!(:zero_order) {
+        create(:order, state: "payment", line_items: [create(:line_item, price: 0)])
+      }
+      let!(:zero_payment) { create(:payment, order: zero_order, amount: 0, state: "checkout") }
+      let(:updater) { OrderManagement::Order::Updater.new(zero_order) }
+
+      it "processes payments successfully" do
+        zero_order.process_payments!
+        updater.update_payment_state
+
+        expect(zero_order.payment_state).to eq "paid"
+        expect(zero_payment.reload.state).to eq "completed"
+        expect(zero_payment.captured_at).to_not be_nil
+      end
+    end
   end
 end