test: add JUnit test for GildedRose updateQuality logic

- Adds tests covering all item types (Aged Brie, Backstage passes, Sulfuras, normal items),

- Edge cases (quality never below 0 or above 50), and sellIn behavior.

- Includes tests for quality changes before and after sellIn expiration.

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

@@ -1,17 +1,83 @@
 package com.gildedrose;
 
 import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.*;
 
 class GildedRoseTest {
 
-    @Test
-    void foo() {
-        Item[] items = new Item[] { new Item("foo", 0, 0) };
-        GildedRose app = new GildedRose(items);
-        app.updateQuality();
-        assertEquals("fixme", app.items[0].name);
+    private Item createItem(String name, int sellIn, int quality) {
+        return new Item(name, sellIn, quality);
     }
 
+    @Test
+    void normaleItem_QualitaetSinktProTag() {
+        Item item = createItem("Normaler Gegenstand", 10, 20);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(19, item.quality); // -1 Qualität
+    }
+
+    @Test
+    void normaleItem_QualitaetSinktDoppeltNachVerfall() {
+        Item item = createItem("Normaler Gegenstand", 0, 20);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(18, item.quality); // -2 Qualität
+    }
+
+    @Test
+    void agedBrie_QualitaetSteigt() {
+        Item item = createItem("Aged Brie", 10, 20);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(21, item.quality); // +1 Qualität
+    }
+
+    @Test
+    void agedBrie_QualitaetSteigtSchnellerNachVerfall() {
+        Item item = createItem("Aged Brie", -1, 20);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(22, item.quality); // +2 Qualität
+    }
+
+    @Test
+    void backstagePass_QualitaetSteigtUm3Bei5Tagen() {
+        Item item = createItem("Backstage passes to a TAFKAL80ETC concert", 5, 20);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(23, item.quality); // +3 Qualität
+    }
+
+    @Test
+    void backstagePass_QualitaetFälltAuf0NachKonzert() {
+        Item item = createItem("Backstage passes to a TAFKAL80ETC concert", 0, 20);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(0, item.quality); // Qualität = 0
+    }
+
+    @Test
+    void sulfuras_QualitaetUnverändert() {
+        Item item = createItem("Sulfuras, Hand of Ragnaros", 10, 80);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(80, item.quality); // Qualität bleibt 80
+    }
+
+    @Test
+    void qualitaetNieÜber50() {
+        Item item = createItem("Aged Brie", 10, 50);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(50, item.quality); // Maximalwert 50
+    }
+
+    @Test
+    void qualitaetNieUnter0() {
+        Item item = createItem("Normaler Gegenstand", 10, 0);
+        GildedRose app = new GildedRose(new Item[]{item});
+        app.updateQuality();
+        assertEquals(0, item.quality); // Minimalwert 0
+    }
 }