From fe4145d9d561aaffbf089b3bbdb5377212f0886f Mon Sep 17 00:00:00 2001
From: Rob Harrington <oeoeaio@gmail.com>
Date: Fri, 2 Mar 2018 11:40:20 +1100
Subject: [PATCH 1/2] Use expect syntax

---
 spec/models/spree/line_item_spec.rb | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/spec/models/spree/line_item_spec.rb b/spec/models/spree/line_item_spec.rb
index 61c4ca0f23..2d32674d0f 100644
--- a/spec/models/spree/line_item_spec.rb
+++ b/spec/models/spree/line_item_spec.rb
@@ -52,28 +52,28 @@ module Spree
 
       it "caps quantity" do
         li.cap_quantity_at_stock!
-        li.reload.quantity.should == 5
+        expect(li.reload.quantity).to eq 5
       end
 
       it "does not cap max_quantity" do
         li.cap_quantity_at_stock!
-        li.reload.max_quantity.should == 10
+        expect(li.reload.max_quantity).to eq 10
       end
 
       it "works for products without max_quantity" do
         li.update_column :max_quantity, nil
         li.cap_quantity_at_stock!
         li.reload
-        li.quantity.should == 5
-        li.max_quantity.should be_nil
+        expect(li.quantity).to eq 5
+        expect(li.max_quantity).to be nil
       end
 
       it "does nothing for on_demand items" do
         v.update_attributes! on_demand: true
         li.cap_quantity_at_stock!
         li.reload
-        li.quantity.should == 10
-        li.max_quantity.should == 10
+        expect(li.quantity).to eq 10
+        expect(li.max_quantity).to eq 10
       end
 
       context "when a variant override is in place" do
@@ -90,7 +90,7 @@ module Spree
 
         it "caps quantity to override stock level" do
           li.cap_quantity_at_stock!
-          li.quantity.should == 2
+          expect(li.quantity).to eq 2
         end
       end
     end

From 28491ee94882c315d7bd0fca8bdf315f5c8256e0 Mon Sep 17 00:00:00 2001
From: Rob Harrington <oeoeaio@gmail.com>
Date: Fri, 2 Mar 2018 12:03:12 +1100
Subject: [PATCH 2/2] Skip stock check when requested quantity is zero

This prevents an error being raised when available stock is negative
---
 app/models/spree/line_item_decorator.rb |  2 ++
 spec/models/spree/line_item_spec.rb     | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/app/models/spree/line_item_decorator.rb b/app/models/spree/line_item_decorator.rb
index 6250530c51..11c9d36850 100644
--- a/app/models/spree/line_item_decorator.rb
+++ b/app/models/spree/line_item_decorator.rb
@@ -131,7 +131,9 @@ Spree::LineItem.class_eval do
 
   # MONKEYPATCH of Spree method
   # Enables scoping of variant to hub/shop, so we check stock against relevant overrides if they exist
+  # Also skips stock check if requested quantity is zero
   def sufficient_stock?
+    return true if quantity == 0 # This line added
     scoper.scope(variant) # This line added
     return true if Spree::Config[:allow_backorders]
     if new_record? || !order.completed?
diff --git a/spec/models/spree/line_item_spec.rb b/spec/models/spree/line_item_spec.rb
index 2d32674d0f..cb1755f60c 100644
--- a/spec/models/spree/line_item_spec.rb
+++ b/spec/models/spree/line_item_spec.rb
@@ -76,6 +76,12 @@ module Spree
         expect(li.max_quantity).to eq 10
       end
 
+      it "caps at zero when stock is negative" do
+        v.update_attributes(on_hand: -2)
+        li.cap_quantity_at_stock!
+        expect(li.reload.quantity).to eq 0
+      end
+
       context "when a variant override is in place" do
         let!(:hub) { create(:distributor_enterprise) }
         let!(:vo) { create(:variant_override, hub: hub, variant: v, count_on_hand: 2) }
@@ -92,6 +98,16 @@ module Spree
           li.cap_quantity_at_stock!
           expect(li.quantity).to eq 2
         end
+
+        context "when count on hand is negative" do
+          before { vo.update_attributes(count_on_hand: -3) }
+
+          it "caps at zero" do
+            v.update_attributes(on_hand: -2)
+            li.cap_quantity_at_stock!
+            expect(li.reload.quantity).to eq 0
+          end
+        end
       end
     end