feat: add AgedBrieStrategy

python/gilded_rose.py

@@ -27,6 +27,22 @@ class NormalStrategy:
                 item.quality = max(0, item.quality - 1)
 
 
+class AgedBrieStrategy:
+    """
+    Quality improvement strategy for Aged Brie.
+
+    Quality increases by 1 per day; by 2 per day once the sell date
+    has passed. Quality never exceeds 50.
+    """
+
+    def update(self, item: "Item", days: int) -> None:
+        for _ in range(days):
+            item.quality = min(50, item.quality + 1)
+            item.sell_in -= 1
+            if item.sell_in < 0:
+                item.quality = min(50, item.quality + 1)
+
+
 class GildedRose(object):
 
     def __init__(self, items):

python/tests/test_gilded_rose.py

@@ -7,7 +7,7 @@ _EXERCISE_ROOT = Path(__file__).resolve().parent.parent
 if str(_EXERCISE_ROOT) not in sys.path:
     sys.path.insert(0, str(_EXERCISE_ROOT))
 
-from gilded_rose import Item, GildedRose, NormalStrategy
+from gilded_rose import Item, GildedRose, NormalStrategy, AgedBrieStrategy
 
 
 class GildedRoseTest(unittest.TestCase):
@@ -59,5 +59,38 @@ class TestNormalStrategy(unittest.TestCase):
         self.assertEqual(0, item.quality)
 
 
+class TestAgedBrieStrategy(unittest.TestCase):
+    """Tests for AgedBrieStrategy — quality improves with age."""
+
+    def setUp(self):
+        self.strategy = AgedBrieStrategy()
+
+    def test_quality_increments_by_one_each_day(self):
+        item = Item("Aged Brie", sell_in=10, quality=20)
+        self.strategy.update(item, days=1)
+        self.assertEqual(21, item.quality)
+        self.assertEqual(9, item.sell_in)
+
+    def test_quality_caps_at_50(self):
+        item = Item("Aged Brie", sell_in=10, quality=50)
+        self.strategy.update(item, days=1)
+        self.assertEqual(50, item.quality)
+
+    def test_quality_increments_twice_after_sell_date(self):
+        # Past sell date: +2 per day
+        item = Item("Aged Brie", sell_in=0, quality=20)
+        self.strategy.update(item, days=1)
+        self.assertEqual(22, item.quality)
+        self.assertEqual(-1, item.sell_in)
+
+    def test_multi_day_crosses_sell_date(self):
+        # sell_in=1, quality=46, days=3
+        # Day1: q=47 si=0 | Day2: q=49 si=-1 | Day3: q=50 (capped) si=-2
+        item = Item("Aged Brie", sell_in=1, quality=46)
+        self.strategy.update(item, days=3)
+        self.assertEqual(50, item.quality)
+        self.assertEqual(-2, item.sell_in)
+
+
 if __name__ == '__main__':
     unittest.main()