Quality is never more than 50 (except Sulfuras).

Kotlin/src/test/kotlin/com/gildedrose/GildedRoseTest.kt

@@ -47,6 +47,20 @@ internal class GildedRoseTest {
         }
     }
 
+    @Test
+    fun qualityIsNeverMoreThanFifty() {
+        (items.map { it.sellIn }.maxOrNull()!! downTo -3).forEach {
+            gildedRose.updateQuality()
+            assertFalse(
+                items
+                    .filterNot { it.name.startsWith("Sulfuras") }
+                    .map { it.quality }
+                    .maxOrNull()!!
+                        > 50
+            )
+        }
+    }
+
     @Test
     fun ordinaryItemsDecreaseInSellIn() {
         val elixir = gildedRose.items.first { it.name.startsWith("Elixir") }