Add Unit Tests to initial cases

Java/src/test/java/com/gildedrose/GildedRoseTest.java

@@ -14,4 +14,57 @@ class GildedRoseTest {
         assertEquals("foo", app.items[0].name);
     }
 
+    @Test
+    void degradesTwiceAsFastAfterSellInDateHasPassed() {
+        Item[] items = new Item[]{new Item("foo", 0, 2)};
+        new GildedRose(items).updateQuality();
+        assertEquals(0, items[0].quality);
+    }
+
+    @Test
+    void neverMustHaveNegativeQuality() {
+        Item[] items = new Item[]{new Item("foo", 0, 0)};
+        new GildedRose(items).updateQuality();
+        assertEquals(0, items[0].quality);
+    }
+
+    @Test
+    void increaseAgedBrieQualityWhenItGetsOlder() {
+        Item[] items = new Item[]{new Item("Aged Brie", 0, 2)};
+        new GildedRose(items).updateQuality();
+        assertEquals(4, items[0].quality);
+    }
+
+    @Test
+    void neverMustHaveAnItemWithMoreThan50OfQuality() {
+        Item[] items = new Item[]{new Item("Aged Brie", 0, 50)};
+        new GildedRose(items).updateQuality();
+        assertEquals(50, items[0].quality);
+    }
+
+
+    @Test
+    void neverModifySulfurasQuality() {
+        Item[] items = new Item[]{new Item("Sulfuras, Hand of Ragnaros", 0, 50)};
+        new GildedRose(items).updateQuality();
+        assertEquals(50, items[0].quality);
+    }
+
+    @Test
+    void neverModifySulfurasQualityEvenISGreaterThan50() {
+        Item[] items = new Item[]{new Item("Sulfuras, Hand of Ragnaros", 0, 80)};
+        new GildedRose(items).updateQuality();
+        assertEquals(80, items[0].quality);
+    }
+
+    @Test
+    void mustIncreaseBackstagePassesQualityWhenItsSellInApproaches() {
+        Item[] items = new Item[]{new Item("Backstage passes to a TAFKAL80ETC concert", 15, 20),
+            new Item("Backstage passes to a TAFKAL80ETC concert", 10, 20),
+            new Item("Backstage passes to a TAFKAL80ETC concert", 5, 20)};
+        new GildedRose(items).updateQuality();
+        assertEquals(21, items[0].quality);
+        assertEquals(22, items[1].quality);
+        assertEquals(23, items[2].quality);
+    }
 }