Fix line items returning prices with fractional cents

app/models/spree/line_item_decorator.rb

@@ -26,7 +26,7 @@ Spree::LineItem.class_eval do
   def price_with_adjustments
     # EnterpriseFee#create_locked_adjustment applies adjustments on line items to their parent order,
     # so line_item.adjustments returns an empty array
-    price + order.adjustments.where(source_id: id).sum(&:amount) / quantity
+    (price + order.adjustments.where(source_id: id).sum(&:amount) / quantity).round(2)
   end
 
   def single_display_amount_with_adjustments
@@ -34,9 +34,9 @@ Spree::LineItem.class_eval do
   end
 
   def amount_with_adjustments
-    # EnterpriseFee#create_locked_adjustment applies adjustments on line items to their parent order,
-    # so line_item.adjustments returns an empty array
-    amount + order.adjustments.where(source_id: id).sum(&:amount)
+    # We calculate from price_with_adjustments here rather than building our own value because
+    # rounding errors can produce discrepencies of $0.01.
+    price_with_adjustments * quantity
   end
 
   def display_amount_with_adjustments

spec/models/spree/line_item_spec.rb

@@ -25,5 +25,27 @@ module Spree
         LineItem.supplied_by_any([s1, s2]).sort.should == [li1, li2].sort
       end
     end
+
+    describe "calculating price with adjustments" do
+      it "does not return fractional cents" do
+        li = LineItem.new
+
+        li.stub(:price) { 55.55 }
+        li.stub_chain(:order, :adjustments, :where, :sum) { 11.11 }
+        li.stub(:quantity) { 2 }
+        li.price_with_adjustments.should == 61.11
+      end
+    end
+
+    describe "calculating amount with adjustments" do
+      it "returns a value consistent with price_with_adjustments" do
+        li = LineItem.new
+
+        li.stub(:price) { 55.55 }
+        li.stub_chain(:order, :adjustments, :where, :sum) { 11.11 }
+        li.stub(:quantity) { 2 }
+        li.amount_with_adjustments.should == 122.22
+      end
+    end
   end
 end