Add regression_test that uses https://github.com/approvals/ApprovalTests.Java to verify the system's output against Golden Master.

Uses alternative ApprovalTests approach suggested by LlewellynFalco.
When you add JUnit to the classpath to get GildedRoseTest to run, also add ApprovalTests.jar, found in the latest zip @ https://github.com/approvals/ApprovalTests.Java/releases.

Java/com/gildedrose/GildedRose.java

@@ -1,5 +1,10 @@
 package com.gildedrose;
 
+import java.util.Arrays;
+import java.util.LinkedList;
+
+import static java.util.stream.Collectors.toList;
+
 class GildedRose {
     Item[] items;
 
@@ -59,4 +64,10 @@ class GildedRose {
             }
         }
     }
+
+    @Override
+    public String toString()
+    {
+        return Arrays.stream(items).collect(toList()).toString();
+    }
 }

Java/com/gildedrose/GildedRoseTest.java

@@ -1,17 +1,82 @@
 package com.gildedrose;
 
+import static java.lang.Integer.*;
+import static java.lang.Integer.MIN_VALUE;
+import static java.util.function.Function.identity;
 import static org.junit.Assert.*;
 
+import org.approvaltests.legacycode.LegacyApprovals;
+import org.approvaltests.reporters.DiffReporter;
+import org.approvaltests.reporters.JunitReporter;
+import org.approvaltests.reporters.UseReporter;
 import org.junit.Test;
 
+import java.util.Arrays;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+@UseReporter(JunitReporter.class)
 public class GildedRoseTest {
 
+    Stream<String> ODD_ITEM_NAMES = Σ("", "pie", "foo");
+    Stream<String> KNOWN_ITEM_NAMES =
+         Σ("Aged Brie",
+           "Elixir of the Mongoose",
+           "Sulfuras, Hand of Ragnaros",
+           "Backstage passes to a TAFKAL80ETC concert");
+    Stream<String> UNKNOWN_ITEM_NAMES = Σ("+5 Dexterity Vest", "Conjured Mana Cake");
+
+    Stream<Integer> MIN_DAYS =                Σ(MIN_VALUE);
+    Stream<Integer> DAYS_NEAR_ZERO =          Σ(-1,0,1);
+    Stream<Integer> SINGLE_DIGIT_DAYS =       Σ(4,5,6);
+    Stream<Integer> LOW_DOUBLE_DIGIT_DAYS =   Σ(10,11,12);
+    Stream<Integer> HIGH_DOUBLE_DIGIT_DAYS =  Σ(99_999,100_000,100_001);
+    Stream<Integer> MAX_DAYS =                Σ(MAX_VALUE);
+
+    Stream<Integer> MINIMUM_QUALITY =         Σ(0);
+    Stream<Integer> SINGLE_DIGIT_QUALITIES =  Σ(1,2,3,4,5);
+    Stream<Integer> DOUBLE_DIGIT_QUALITIES =  Σ(12,13,15);
+    Stream<Integer> QUALITIES_NEAR_MAXIMUM =  Σ(47,48,49);
+    Stream<Integer> MAXIMUM_QUALITY =         Σ(50);
+    Stream<Integer> LEGENDARY_ITEM_QUALITY =  Σ(80);
+
+    Stream<String>  GOOD_MIX_OF_ITEM_NAMES =
+            ⁀(ODD_ITEM_NAMES, KNOWN_ITEM_NAMES, UNKNOWN_ITEM_NAMES);
+    Stream<Integer> GOOD_MIX_OF_NUMBER_OF_DAYS_BY_WHICH_TO_SELL_ITEM =
+            ⁀(MIN_DAYS, DAYS_NEAR_ZERO, SINGLE_DIGIT_DAYS, LOW_DOUBLE_DIGIT_DAYS, HIGH_DOUBLE_DIGIT_DAYS, MAX_DAYS);
+    Stream<Integer> GOOD_MIX_OF_ITEM_QUALITY_LEVELS =
+            ⁀(MINIMUM_QUALITY, SINGLE_DIGIT_QUALITIES, DOUBLE_DIGIT_QUALITIES, QUALITIES_NEAR_MAXIMUM, MAXIMUM_QUALITY, LEGENDARY_ITEM_QUALITY);
+
     @Test
     public void foo() {
-        Item[] items = new Item[] { new Item("foo", 0, 0) };
-        GildedRose app = new GildedRose(items);
-        app.updateQuality();
+        String name = "foo";
+        int sellIn = 0;
+        int quality = 0;
+        GildedRose app = updateQuality(name, sellIn, quality);
         assertEquals("fixme", app.items[0].name);
     }
 
+    @Test
+    public void regression_test() throws Exception
+    {
+        String[] names = GOOD_MIX_OF_ITEM_NAMES.toArray(String[]::new);
+        Integer[] sellIn = GOOD_MIX_OF_NUMBER_OF_DAYS_BY_WHICH_TO_SELL_ITEM.toArray(Integer[]::new);
+        Integer[] quality = GOOD_MIX_OF_ITEM_QUALITY_LEVELS.toArray(Integer[]::new);
+        LegacyApprovals.LockDown(this, "updateQuality", names, sellIn, quality);
+    }
+
+    public GildedRose updateQuality(String name, Integer sellIn, Integer quality)
+    {
+        Item[] items = new Item[] { new Item(name, sellIn, quality) };
+        GildedRose app = new GildedRose(items);
+        app.updateQuality();
+        return app;
+    }
+
+    // Create a stream of As
+    private <A> Stream<A> Σ(A... As){ return Arrays.stream(As); }
+
+    // concatenate streams of As
+    private <A> Stream<A> ⁀(Stream<A>... streams) { return Arrays.stream(streams).flatMap( Function.identity() ); }
+
 }