Add a similar test to classic ItemsSketchTest

src/test/java/org/apache/datasketches/kll/KllItemsSketchTest.java

@@ -730,11 +730,22 @@ public void checkExceptions() {
     try { sk2.setN(0); fail(); } catch (SketchesArgumentException e) { }
   }
 
+  @Test
+  public void checkSortedViewAfterReset() {
+    KllItemsSketch<String> sk = KllItemsSketch.newHeapInstance(20, Comparator.naturalOrder(), serDe);
+    sk.update("1");
+    GenericSortedView<String> sv = sk.getSortedView();
+    String ssv = sv.getQuantile(1.0, INCLUSIVE);
+    assertEquals(ssv, "1");
+    sk.reset();
+    try { sk.getSortedView(); fail(); } catch (SketchesArgumentException e) { }
+  }
+
   @Test
   //There is no guarantee that L0 is sorted after a merge.
   //The issue is, during a merge, L0 must be sorted prior to a compaction to a higher level.
   //Otherwise the higher levels would not be sorted properly.
-  public void checkL0SortDuringMerge() throws NumberFormatException {
+  public void checkL0SortDuringMergeIssue527() throws NumberFormatException {
     final Random rand = new Random();
     final KllItemsSketch<String> sk1 = KllItemsSketch.newHeapInstance(8, Comparator.reverseOrder(), serDe);
     final KllItemsSketch<String> sk2 = KllItemsSketch.newHeapInstance(8, Comparator.reverseOrder(), serDe);
@@ -759,18 +770,6 @@ public void checkL0SortDuringMerge() throws NumberFormatException {
     }
   }
 
-  @Test
-  public void checkSortedViewAfterReset() {
-    KllItemsSketch<String> sk = KllItemsSketch.newHeapInstance(20, Comparator.naturalOrder(), serDe);
-    sk.update("1");
-    GenericSortedView<String> sv = sk.getSortedView();
-    String ssv = sv.getQuantile(1.0, INCLUSIVE);
-    assertEquals(ssv, "1");
-    sk.reset();
-    try { sk.getSortedView(); fail(); } catch (SketchesArgumentException e) { }
-  }
-
-
   private final static boolean enablePrinting = false;
 
   /**

src/test/java/org/apache/datasketches/quantiles/ItemsSketchTest.java

@@ -20,6 +20,7 @@
 package org.apache.datasketches.quantiles;
 
 import static org.apache.datasketches.quantiles.PreambleUtil.DEFAULT_K;
+import static org.apache.datasketches.quantilescommon.LongsAsOrderableStrings.getString;
 import static org.apache.datasketches.quantilescommon.QuantileSearchCriteria.EXCLUSIVE;
 import static org.apache.datasketches.quantilescommon.QuantileSearchCriteria.INCLUSIVE;
 import static org.testng.Assert.assertEquals;
@@ -30,6 +31,7 @@
 
 import java.util.Arrays;
 import java.util.Comparator;
+import java.util.Random;
 
 import org.apache.datasketches.common.ArrayOfBooleansSerDe;
 import org.apache.datasketches.common.ArrayOfDoublesSerDe;
@@ -42,6 +44,7 @@
 import org.apache.datasketches.quantilescommon.GenericSortedView;
 import org.apache.datasketches.quantilescommon.GenericSortedViewIterator;
 import org.apache.datasketches.quantilescommon.ItemsSketchSortedView;
+import org.apache.datasketches.quantilescommon.QuantilesGenericSketchIterator;
 import org.testng.annotations.BeforeMethod;
 import org.testng.annotations.Test;
 
@@ -663,6 +666,43 @@ private static <T> void checkSketchesEqual(ItemsSketch<T> expected, ItemsSketch<
     assertEquals(actItemsArr, expItemsArr);
   }
 
+  @Test
+  //There is no guarantee that BaseBuffer is sorted after a merge.
+  //The issue is, during a merge, BB must be sorted prior to a compaction to a higher level.
+  //Otherwise the higher levels would not be sorted properly.
+  public void checkL0SortDuringMergeIssue527() throws NumberFormatException {
+    final Random rand = new Random();
+    final ItemsSketch<String> sk1 = ItemsSketch.getInstance(String.class, 8, Comparator.reverseOrder());
+    final ItemsSketch<String> sk2 = ItemsSketch.getInstance(String.class, 8, Comparator.reverseOrder());
+    final int n = 24; //don't change this
+    for (int i = 1; i <= n; i++ ) {
+      final int j = rand.nextInt(n) + 1;
+      sk1.update(getString(j, 3));
+      sk2.update(getString(j +100, 3));
+    }
+    int k = 8;
+    ItemsUnion<String> union = ItemsUnion.getInstance(String.class, k, Comparator.reverseOrder());
+    union.union(sk1);
+    union.union(sk2);
+    ItemsSketch<String> sk3 = union.getResult();
+    println(sk3.toString(true, true)); //L0 and above should be sorted in reverse. Ignore BB.
+
+    final QuantilesGenericSketchIterator<String> itr = sk3.iterator();
+    itr.next();
+    int prev = Integer.parseInt(itr.getQuantile().trim());
+    for (int i = 1; i < (2 * k); i++) {
+      if (itr.next()) {
+        int v = Integer.parseInt(itr.getQuantile().trim());
+        if (i == k) {
+          prev = Integer.parseInt(itr.getQuantile().trim());
+          continue;
+        }
+        assertTrue(v <= prev);
+        prev = v;
+      }
+    }
+  }
+
   @Test
   public void printlnTest() {
     println("PRINTING: "+this.getClass().getName());