Extract 'Aged Brie'

Also noticed I made a mistake in some specs, would normally optimise spec code later on.
Added an extra test for when sell_in is 1 for safety as it depends on the order of operations in the extraction I make.

ruby/gilded_rose.rb

@@ -7,6 +7,8 @@ class GildedRose
   def update_quality
     @items.each do |item|
       case item.name
+      when 'Aged Brie'
+        update_aged_brie_quality(item)
       when 'Sulfuras, Hand of Ragnaros'
         update_sulfuras_quality(item)
       else
@@ -51,6 +53,14 @@ class GildedRose
     end
   end
 
+  def update_aged_brie_quality(item)
+    item.sell_in -= 1
+
+    item.quality += 1
+    item.quality += 1 if item.sell_in.negative?
+    item.quality = 50 if item.quality > 50
+  end
+
   def update_sulfuras_quality(item); end
 end
 

ruby/specs/gilded_rose_spec.rb

@@ -37,6 +37,20 @@ describe GildedRose do
         end
       end
 
+      context 'when 1 day left' do
+        let(:sell_in) { 1 }
+
+        it 'lowers quality by 1' do
+          subject.update_quality
+          expect(items[0].quality).to eq 2
+        end
+
+        it 'lowers sell_in by 1' do
+          subject.update_quality
+          expect(items[0].sell_in).to eq 0
+        end
+      end
+
       it 'does never lower the quality below 0' do
         items = [Item.new(item_name, sell_in, 0)]
         subject.update_quality
@@ -60,6 +74,20 @@ describe GildedRose do
         end
       end
 
+      context 'when 1 day left' do
+        let(:sell_in) { 1 }
+
+        it 'does not lower quality by 1' do
+          subject.update_quality
+          expect(items[0].quality).to eq 80
+        end
+
+        it 'does not lower sell_in' do
+          subject.update_quality
+          expect(items[0].sell_in).to eq 1
+        end
+      end
+
       context 'when sell by date has passed' do
         let(:sell_in) { 0 }
 
@@ -104,9 +132,23 @@ describe GildedRose do
         end
       end
 
+      context 'when 1 day left' do
+        let(:sell_in) { 1 }
+
+        it 'increases quality by 1' do
+          subject.update_quality
+          expect(items[0].quality).to eq 4
+        end
+
+        it 'lowers sell_in by 1' do
+          subject.update_quality
+          expect(items[0].sell_in).to eq 0
+        end
+      end
+
       it 'does never raise the quality above 50' do
         items = [Item.new(item_name, sell_in, 50)]
-        subject.update_quality
+        GildedRose.new(items).update_quality
         expect(items[0].quality).to eq 50
       end
     end
@@ -143,6 +185,20 @@ describe GildedRose do
         end
       end
 
+      context 'when 1 day left' do
+        let(:sell_in) { 1 }
+
+        it 'increases quality by 1' do
+          subject.update_quality
+          expect(items[0].quality).to eq 6
+        end
+
+        it 'lowers sell_in by 1' do
+          subject.update_quality
+          expect(items[0].sell_in).to eq 0
+        end
+      end
+
       context 'when sell by date has passed' do
         let(:sell_in) { 0 }
 
@@ -159,7 +215,7 @@ describe GildedRose do
 
       it 'does never raise the quality above 50' do
         items = [Item.new(item_name, sell_in, 50)]
-        subject.update_quality
+        GildedRose.new(items).update_quality
         expect(items[0].quality).to eq 50
       end
     end
@@ -179,6 +235,20 @@ describe GildedRose do
         end
       end
 
+      context 'when 1 day left' do
+        let(:sell_in) { 1 }
+
+        it 'lowers quality by 2' do
+          subject.update_quality
+          expect(items[0].quality).to eq 1
+        end
+
+        it 'lowers sell_in by 1' do
+          subject.update_quality
+          expect(items[0].sell_in).to eq 2
+        end
+      end
+
       context 'when sell by date has passed' do
         let(:sell_in) { 0 }
         let(:quality) { 6 }
@@ -196,7 +266,7 @@ describe GildedRose do
 
       it 'does never lower the quality below 0' do
         items = [Item.new(item_name, sell_in, 0)]
-        subject.update_quality
+        GildedRose.new(items).update_quality
         expect(items[0].quality).to eq 0
       end
     end