VariantOverride with on_demand now overriding stock

Otherwise we would try to take stock from the producer stock level
without respecting their on-demand settings. So from now on:
If stock level or on_demand are set on the override then it's not using
producer stock levels.

app/models/concerns/stock_settings_override_validation.rb

@@ -10,7 +10,7 @@
 #
 # | on_demand | count_on_hand | stock_overridden? | use_producer_stock_settings? | valid? |
 # |-----------|---------------|-------------------|------------------------------|--------|
-# | 1         | nil           | false             | false                        | true   |
+# | 1         | nil           | true              | false                        | true   |
 # | 0         | x             | true              | false                        | true   |
 # | nil       | nil           | false             | true                         | true   |
 # | 1         | x             | true              | false                        | true   |

app/models/concerns/variant_stock.rb

@@ -96,7 +96,7 @@ def can_supply?(quantity)
   # Here we depend only on variant.total_on_hand and variant.on_demand.
   #   This way, variant_overrides only need to override variant.total_on_hand and variant.on_demand.
   def fill_status(quantity)
-    on_hand = if total_on_hand >= quantity || on_demand
+    on_hand = if total_on_hand.to_i >= quantity || on_demand
                 quantity
               else
                 [0, total_on_hand].max

app/models/variant_override.rb

@@ -38,9 +38,8 @@ def self.indexed(hub)
   end
 
   def stock_overridden?
-    # If count_on_hand is present, it means on_demand is false
-    #   See StockSettingsOverrideValidation for details
-    count_on_hand.present?
+    # Testing for not nil because for a boolean `false.present?` is false.
+    !on_demand.nil? || !count_on_hand.nil?
   end
 
   def use_producer_stock_settings?

spec/lib/open_food_network/scope_variant_to_hub_spec.rb

@@ -181,11 +181,10 @@ module OpenFoodNetwork
             scoper.scope v2
           end
 
-          it "doesn't reduce variant's stock" do
-            pending "updating override stock"
-
+          it "reduces override stock, not variant's stock" do
             v2.move(-2)
             expect(Spree::Variant.find(v2.id).on_hand).to eq 5
+            expect(v2.on_hand).to eq(-2)
           end
         end
 

spec/models/spree/variant_stock_spec.rb

@@ -82,16 +82,14 @@
       end
 
       it "doesn't fail on negative stock when on demand" do
-        pending "https://github.com/openfoodfoundation/openfoodnetwork/issues/12586"
-
         override.update!(on_demand: true, count_on_hand: nil)
 
         expect {
           hub_variant.move(-8)
           override.reload
         }
-          .to change { override.count_on_hand }.from(7).to(-1)
-          .and change { hub_variant.on_hand }.from(7).to(-1)
+          .to change { override.count_on_hand }.from(nil).to(-8)
+          .and change { hub_variant.on_hand }.from(nil).to(-8)
           .and change { variant.on_hand }.by(0)
       end
     end

spec/models/variant_override_spec.rb

@@ -165,7 +165,7 @@
 
   describe "with nil count on hand" do
     let(:variant_override) do
-      build_stubbed(
+      build(
         :variant_override,
         variant: build_stubbed(:variant),
         hub: build_stubbed(:distributor_enterprise),
@@ -175,15 +175,18 @@
     end
 
     describe "stock_overridden?" do
-      it "returns false" do
-        expect(variant_override.stock_overridden?).to be false
+      it "returns true" do
+        expect(variant_override.stock_overridden?).to be true
       end
     end
 
     describe "move_stock!" do
       it "silently logs an error" do
-        expect(Bugsnag).to receive(:notify)
-        variant_override.move_stock!(5)
+        expect {
+          variant_override.move_stock!(5)
+        }.to change {
+          variant_override.count_on_hand
+        }.from(nil).to(5)
       end
     end
   end

spec/system/consumer/shopping/variant_overrides_spec.rb

@@ -222,15 +222,13 @@
       expect(product1_variant1_override.reload.count_on_hand).to be_nil
     end
 
-    it "does not subtract stock from variants where the override has on_demand: true" do
-      pending "update override stock"
-
+    it "subtracts stock from override but not variants where the override has on_demand: true" do
       click_add_to_cart product4_variant1, 2
       click_checkout
       expect do
         complete_checkout
       end.to change { product4_variant1.reload.on_hand }.by(0)
-      expect(product4_variant1_override.reload.count_on_hand).to be_nil
+      expect(product4_variant1_override.reload.count_on_hand).to eq(-2)
     end
 
     it "does not show out of stock flags on order confirmation page" do