Fix usage of variant.on_hand in subscriptions order factory, we now take on_demand into account

This fixes a problem introduced in 12eab1bfa9 (diff-c3c4192f302cc77e9a8547012fe86ddb), since then variant.on_hand does not return infinity if variant is on_demand

app/services/order_factory.rb

@@ -48,7 +48,7 @@ class OrderFactory
     attrs[:line_items].each do |li|
       next unless variant = Spree::Variant.find_by_id(li[:variant_id])
       scoper.scope(variant)
-      li[:quantity] = stock_limited_quantity(variant.on_hand, li[:quantity])
+      li[:quantity] = stock_limited_quantity(variant.on_demand, variant.on_hand, li[:quantity])
       li[:price] = variant.price
       build_item_from(li)
     end
@@ -81,9 +81,9 @@ class OrderFactory
     @order.payments.create(payment_method_id: attrs[:payment_method_id], amount: @order.reload.total)
   end
 
-  def stock_limited_quantity(stock, requested)
-    return requested if opts[:skip_stock_check]
-    [stock, requested].min
+  def stock_limited_quantity(variant_on_demand, variant_on_hand, requested)
+    return requested if opts[:skip_stock_check] || variant_on_demand
+    [variant_on_hand, requested].min
   end
 
   def scoper

spec/services/order_factory_spec.rb

@@ -31,7 +31,7 @@ describe OrderFactory do
       attrs
     end
 
-    it "builds a new order based the provided attributes" do
+    it "builds a new order based on the provided attributes" do
       expect{ order }.to change{ Spree::Order.count }.by(1)
       expect(order).to be_a Spree::Order
       expect(order.line_items.count).to eq 2
@@ -78,11 +78,21 @@ describe OrderFactory do
         end
 
         context "when skip_stock_check is not requested" do
-          it "initialised the order but limits stock to the available amount" do
+          it "initialises the order but limits stock to the available amount" do
             expect{ order }.to change{ Spree::Order.count }.by(1)
             expect(order).to be_a Spree::Order
             expect(order.line_items.find_by_variant_id(variant1.id).quantity).to eq 2
           end
+
+          context "when variant is on_demand" do
+            before { variant1.update_attribute(:on_demand, true) }
+
+            it "initialises the order with the requested quantity regardless of stock" do
+              expect{ order }.to change{ Spree::Order.count }.by(1)
+              expect(order).to be_a Spree::Order
+              expect(order.line_items.find_by_variant_id(variant1.id).quantity).to eq 5
+            end
+          end
         end
 
         context "when skip_stock_check is requested" do