Display variant price differences as absolute, not relative values

app/helpers/spree/products_helper_decorator.rb

@@ -0,0 +1,9 @@
+module Spree
+  ProductsHelper.class_eval do
+    # Return the price of the variant, or nil if it is identical to the master price
+    def variant_price_diff(variant)
+      return nil if variant.price == variant.product.price
+      "(#{number_to_currency variant.price})"
+    end
+  end
+end

spec/helpers/products_helper_spec.rb

@@ -0,0 +1,35 @@
+require 'spec_helper'
+
+module Spree
+  describe ProductsHelper do
+    subject do
+      obj = Object.new
+      obj.extend(ProductsHelper)
+      obj.extend(ActionView::Helpers::NumberHelper)
+    end
+
+
+    it "displays variant price differences as absolute, not relative values" do
+      variant = make_variant_stub(10.00, 10.00)
+      subject.variant_price_diff(variant).should be_nil
+
+      variant = make_variant_stub(10.00, 15.55)
+      subject.variant_price_diff(variant).should == "($15.55)"
+
+      variant = make_variant_stub(10.00, 5.55)
+      subject.variant_price_diff(variant).should == "($5.55)"
+    end
+
+    private
+    def make_variant_stub(product_price, variant_price)
+      product = stub(:product)
+      product.stub(:price).and_return(product_price)
+
+      variant = stub(:variant)
+      variant.stub(:product).and_return(product)
+      variant.stub(:price).and_return(variant_price)
+
+      variant
+    end
+  end
+end