add random test

Author: rjernst

server/src/main/java/org/elasticsearch/common/util/CollectionUtils.java

@@ -20,6 +20,7 @@
 import java.util.Comparator;
 import java.util.IdentityHashMap;
 import java.util.List;
+import java.util.ListIterator;
 import java.util.Map;
 import java.util.Objects;
 import java.util.RandomAccess;

server/src/test/java/org/elasticsearch/common/util/CollectionUtilsTests.java

@@ -80,6 +80,20 @@ public void testUniquify() {
         assertUniquify(List.of(1, 2, 2, 3), Comparator.naturalOrder(), 3);
         assertUniquify(List.of(1, 2, 2, 2), Comparator.naturalOrder(), 2);
         assertUniquify(List.of(1, 2, 2, 3, 3, 5), Comparator.naturalOrder(), 4);
+
+        for (int i = 0; i < 10; ++i) {
+            int uniqueItems = randomIntBetween(1, 10);
+            var list = new ArrayList<Integer>();
+            int next = 1;
+            for (int j = 0; j < uniqueItems; ++j) {
+                int occurences = randomIntBetween(1, 10);
+                while (occurences-- > 0) {
+                    list.add(next);
+                }
+                next++;
+            }
+            assertUniquify(list, Comparator.naturalOrder(), uniqueItems);
+        }
     }
 
     public void testEmptyPartition() {