--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/java/lang/ThreadLocal/ReplaceStaleEntry.java	Thu Oct 17 13:18:01 2019 +0800
@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8209824
+ * @summary per latest JDK code coverage report, 2 methods replaceStaleEntry
+ *          and prevIndex in ThreadLocal.ThreadLocalMap are not touched
+ *          by any JDK regression tests, this is to trigger the code paths.
+ * @modules java.base/java.lang:+open
+ * @run testng ReplaceStaleEntry
+ */
+
+import java.lang.reflect.Field;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.testng.Assert.assertEquals;
+import org.testng.annotations.BeforeClass;
+import org.testng.annotations.Test;
+
+public class ReplaceStaleEntry {
+
+    public static int INITIAL_CAPACITY;
+
+    @BeforeClass
+    public static void setup() throws Exception {
+        Class<?> clazz = Class.forName("java.lang.ThreadLocal$ThreadLocalMap");
+        Field f = clazz.getDeclaredField("INITIAL_CAPACITY");
+        f.setAccessible(true);
+        INITIAL_CAPACITY = f.getInt(null);
+        System.out.println("INITIAL_CAPACITY: " + INITIAL_CAPACITY);
+    }
+
+    /**
+     * This test triggers the code path to replaceStaleEntry, so as prevIndex is
+     * triggered too as it's called by replaceStaleEntry.
+     * The code paths must be triggered by reusing an already used entry in the
+     * map's entry table. The code below
+     *  1. first occupies the entries
+     *  2. then expunges the entries by removing strong references to thread locals
+     *  3. then reuse some of entries by adding more thread locals to the thread
+     * and, the above steps are run for several times by adding more and more
+     * thread locals, also trigger rehash of the map.
+     */
+    @Test
+    public static void test() {
+        Map<Integer, ThreadLocal> locals = new HashMap<>();
+        for (int j = 1; j < 32; j *= 2) {
+            int loop = INITIAL_CAPACITY * j;
+            for (int i = 0; i < loop; i++) {
+                ThreadLocal l = new ThreadLocal<Integer>();
+                l.set(i);
+                locals.put(i, l);
+            }
+            locals.keySet().stream().forEach(i -> {
+                assertEquals((int)locals.get(i).get(), (int)i, "Unexpected thread local value!");
+            });
+            locals.clear();
+            System.gc();
+        }
+    }
+}