Add test for DefaultQualityBehavior

Java/src/test/java/com/gildedrose/behavior/quality/DefaultQualityBehaviorTest.java

@@ -0,0 +1,45 @@
+package com.gildedrose.behavior.quality;
+
+import com.gildedrose.Item;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class DefaultQualityBehaviorTest {
+
+    private QualityBehavior qualityBehavior;
+
+    @BeforeEach
+    public void setUp() throws Exception {
+        qualityBehavior = new DefaultQualityBehavior();
+    }
+
+    @Test
+    void decreaseQuality() {
+        Item item = getItem(10);
+        qualityBehavior.processQualityUpdate(item);
+
+        assertEquals(9, item.quality);
+    }
+
+    @Test
+    void decreaseNegativeQuality() {
+        Item item = getItem(-10);
+        qualityBehavior.processQualityUpdate(item);
+
+        assertEquals(0, item.quality);
+    }
+
+    @Test
+    void decreaseQualityZero() {
+        Item item = getItem(0);
+        qualityBehavior.processQualityUpdate(item);
+
+        assertEquals(0, item.quality);
+    }
+
+    private Item getItem(int quality) {
+        return new Item("SomeItem", 0, quality);
+    }
+}