When there's an out of stock product in the cart, checkout returns user to cart

app/controllers/checkout_controller.rb

@@ -152,7 +152,7 @@ class CheckoutController < Spree::CheckoutController
   # Overriding Spree's methods
   def raise_insufficient_quantity
     flash[:error] = t(:spree_inventory_error_flash_for_insufficient_quantity)
-    redirect_to main_app.shop_path
+    redirect_to cart_path
   end
 
   def redirect_to_paypal_express_form_if_needed

spec/features/consumer/shopping/checkout_spec.rb

@@ -46,6 +46,22 @@ feature "As a consumer I want to check out my cart", js: true do
       distributor.shipping_methods << sm3
     end
 
+    describe "when I have an out of stock product in my cart" do
+      before do
+        Spree::Config.set allow_backorders: false
+        variant.on_hand = 0
+        variant.save!
+      end
+
+      it "returns me to the cart with an error message" do
+        visit checkout_path
+
+        page.should_not have_selector 'closing', text: "Checkout now"
+        page.should have_selector 'closing', text: "Your shopping cart"
+        page.should have_content "An item in your cart has become unavailable"
+      end
+    end
+
     context "on the checkout page" do
       before do
         visit checkout_path