Add initial tests according to spec for standard items

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

@@ -3,15 +3,70 @@ package com.gildedrose;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
 
 class GildedRoseTest {
 
     @Test
-    void foo() {
-        Item[] items = new Item[] { new Item("foo", 0, 0) };
-        GildedRose app = new GildedRose(items);
+    void updateQuality_standardItem_normalStep() {
+        GildedRose app = createApp(createItem("standard", 10, 15));
         app.updateQuality();
-        assertEquals("fixme", app.items[0].name);
+        assertEquals(9, app.items[0].sellIn);
+        assertEquals(14, app.items[0].quality);
     }
 
+    @Test
+    void updateQuality_standardItem_sellInTo0() {
+        GildedRose app = createApp(createItem("standard", 1, 15));
+        app.updateQuality();
+        assertEquals(0, app.items[0].sellIn);
+        assertEquals(14, app.items[0].quality);
+    }
+
+    @Test
+    void updateQuality_standardItem_minQualityO() {
+        GildedRose app = createApp(createItem("standard", 1, 0));
+        app.updateQuality();
+        assertEquals(0, app.items[0].sellIn);
+        assertEquals(0, app.items[0].quality);
+    }
+
+    @Test
+    void updateQuality_standardItem_doubleDecayAfterLastSellDate() {
+        GildedRose app = createApp(createItem("standard", 0, 10));
+        app.updateQuality();
+        assertEquals(-1, app.items[0].sellIn);
+        assertEquals(8, app.items[0].quality);
+    }
+
+    @Test
+    void updateQuality_standardItem_maxQuality50() {
+        GildedRose app = createApp(createItem("standard", 10, 60));
+
+        app.updateQuality();
+        assertEquals(49, app.items[0].quality);
+    }
+
+    @Test
+    void updateQuality_legendaryItem() {
+        fail("NYI");
+    }
+
+    @Test
+    void updateQuality_agingItem() {
+        fail("NYI");
+    }
+
+    @Test
+    void updateQuality_conjuredItem() {
+        fail("NYI");
+    }
+
+    private GildedRose createApp(Item[] items) {
+        return new GildedRose(items);
+    }
+
+    private Item[] createItem(String name, int sellIn, int quality) {
+        return new Item[] { new Item(name, sellIn, quality) };
+    }
 }