Create class for backstage pass items

Java/src/main/java/com/gildedrose/items/BackstagePassItem.java

@@ -0,0 +1,31 @@
+package com.gildedrose.items;
+
+import com.gildedrose.Quality;
+import com.gildedrose.SellIn;
+import lombok.EqualsAndHashCode;
+
+@EqualsAndHashCode(callSuper = true)
+public class BackstagePassItem extends GildedRoseItem {
+
+  public BackstagePassItem(SellIn sellIn, Quality quality, boolean conjured) {
+    super("Backstage passes to a TAFKAL80ETC concert", sellIn, quality, conjured);
+  }
+
+  @Override
+  protected Quality nextQuality(Quality previous) {
+    Quality nextQuality = previous.copy();
+    if (this.getSellIn().isOver()) {
+      nextQuality.setValue(0);
+      return nextQuality;
+    }
+
+    nextQuality.increment();
+    if (this.getSellIn().daysLeftUntilIsOverAreLessThan(11)) {
+      nextQuality.increment();
+    }
+    if (this.getSellIn().daysLeftUntilIsOverAreLessThan(6)) {
+      nextQuality.increment();
+    }
+    return nextQuality;
+  }
+}

Java/src/test/java/com/gildedrose/items/BackstagePassItemTest.java

@@ -0,0 +1,54 @@
+package com.gildedrose.items;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.gildedrose.Quality;
+import com.gildedrose.SellIn;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+class BackstagePassItemTest {
+
+  @Nested
+  class nextQuality {
+    @Test
+    void should_increment_quality_by_one() {
+      BackstagePassItem item =
+          new BackstagePassItem(SellIn.create(20), Quality.create(0), Boolean.FALSE);
+
+      Quality nextQuality = item.nextQuality(item.getQuality());
+
+      assertThat(nextQuality).isEqualTo(Quality.create(1));
+    }
+
+    @Test
+    void should_increment_quality_by_two_if_less_than_ten_days_to_sell() {
+      BackstagePassItem item =
+          new BackstagePassItem(SellIn.create(10), Quality.create(0), Boolean.FALSE);
+
+      Quality nextQuality = item.nextQuality(item.getQuality());
+
+      assertThat(nextQuality).isEqualTo(Quality.create(2));
+    }
+
+    @Test
+    void should_increment_quality_by_three_if_less_than_five_days_to_sell() {
+      BackstagePassItem item =
+          new BackstagePassItem(SellIn.create(5), Quality.create(0), Boolean.FALSE);
+
+      Quality nextQuality = item.nextQuality(item.getQuality());
+
+      assertThat(nextQuality).isEqualTo(Quality.create(3));
+    }
+
+    @Test
+    void should_set_quality_to_zero_if_sell_is_over() {
+      BackstagePassItem item =
+          new BackstagePassItem(SellIn.create(0), Quality.create(10), Boolean.FALSE);
+
+      Quality nextQuality = item.nextQuality(item.getQuality());
+
+      assertThat(nextQuality).isEqualTo(Quality.create(0));
+    }
+  }
+}