Disallow saving Purchase with a quantity of 0 (#5507)

app/models/purchase.rb

@@ -59,6 +59,7 @@ class Purchase < ApplicationRecord
 
   validates :amount_spent_in_cents, numericality: { greater_than: 0 }
   validate :total_equal_to_all_categories
+  validate :line_items_quantity_is_positive
   before_destroy :check_no_intervening_snapshot
 
   validates :amount_spent_on_diapers_cents, numericality: { greater_than_or_equal_to: 0 }
@@ -140,4 +141,8 @@ def check_no_intervening_snapshot
       raise "We can't delete purchases entered before #{intervening.event_time.to_date}."
     end
   end
+
+  def line_items_quantity_is_positive
+    line_items_quantity_is_at_least(1)
+  end
 end

spec/models/purchase_spec.rb

@@ -65,6 +65,20 @@
       expect(d).not_to be_valid
     end
 
+    it "is not valid if any line item has zero quantity" do
+      item = create(:item)
+      p = build(:purchase)
+      p.line_items.build(item_id: item.id, quantity: 0)
+      expect(p).not_to be_valid
+    end
+
+    it "is not valid if any line item has negative quantity" do
+      item = create(:item)
+      p = build(:purchase)
+      p.line_items.build(item_id: item.id, quantity: -1)
+      expect(p).not_to be_valid
+    end
+
     it "is valid if all categories are positive and add up to the total" do
       d = build(:purchase, amount_spent_in_cents: 1150,
         amount_spent_on_diapers_cents: 200,

spec/queries/low_inventory_query_spec.rb

@@ -34,7 +34,10 @@
   context "when minimum_quantity is 0 and recommended_quantity is nil and item quantity is 0" do
     let(:item) { create :item, organization: organization }
     let(:minimum_quantity) { 0 }
-    let(:inventory_item_quantity) { 0 }
+
+    before do
+      TestInventory.create_inventory(organization, { storage_location.id => { item.id => 0 } })
+    end
 
     it { is_expected.to eq [] }
   end