--- jsr166/src/test/tck/ThreadLocalRandomTest.java	2017/09/19 20:10:49	1.25
+++ jsr166/src/test/tck/ThreadLocalRandomTest.java	2020/08/12 17:39:43	1.30
@@ -63,8 +63,7 @@ public class ThreadLocalRandomTest exten
         ThreadLocalRandom rnd = ThreadLocalRandom.current();
         final java.lang.reflect.Method m;
         try {
-            m = ThreadLocalRandom.class.getDeclaredMethod(
-                    "next", new Class[] { int.class });
+            m = ThreadLocalRandom.class.getDeclaredMethod("next", int.class);
             m.setAccessible(true);
         } catch (SecurityException acceptable) {
             // Security manager may deny access
@@ -355,34 +354,65 @@ public class ThreadLocalRandomTest exten
         // Don't use main thread's ThreadLocalRandom - it is likely to
         // be polluted by previous tests.
         final AtomicReference<ThreadLocalRandom> threadLocalRandom =
-            new AtomicReference<ThreadLocalRandom>();
+            new AtomicReference<>();
         final AtomicLong rand = new AtomicLong();
 
-        long firstRand = 0;
-        ThreadLocalRandom firstThreadLocalRandom = null;
-
         Runnable getRandomState = new CheckedRunnable() {
             public void realRun() {
                 ThreadLocalRandom current = ThreadLocalRandom.current();
                 assertSame(current, ThreadLocalRandom.current());
-                // test bug: the following is not guaranteed and not true in JDK8
-                //                assertNotSame(current, threadLocalRandom.get());
                 rand.set(current.nextLong());
                 threadLocalRandom.set(current);
             }};
 
-        Thread first = newStartedThread(getRandomState);
-        awaitTermination(first);
-        firstRand = rand.get();
-        firstThreadLocalRandom = threadLocalRandom.get();
+        awaitTermination(newStartedThread(getRandomState));
+        long firstRand = rand.get();
+        ThreadLocalRandom firstThreadLocalRandom = threadLocalRandom.get();
+        assertNotNull(firstThreadLocalRandom);
 
         for (int i = 0; i < NCALLS; i++) {
-            Thread t = newStartedThread(getRandomState);
-            awaitTermination(t);
+            awaitTermination(newStartedThread(getRandomState));
+            if (testImplementationDetails)
+                // ThreadLocalRandom has been a singleton since jdk8.
+                assertSame(firstThreadLocalRandom, threadLocalRandom.get());
             if (firstRand != rand.get())
                 return;
         }
         fail("all threads generate the same pseudo-random sequence");
     }
 
+    /**
+     * Repeated calls to nextBytes produce at least values of different signs for every byte
+     */
+    public void testNextBytes() {
+        ThreadLocalRandom rnd = ThreadLocalRandom.current();
+        int n = rnd.nextInt(1, 20);
+        byte[] bytes = new byte[n];
+        outer:
+        for (int i = 0; i < n; i++) {
+            for (int tries = NCALLS; tries-->0; ) {
+                byte before = bytes[i];
+                rnd.nextBytes(bytes);
+                byte after = bytes[i];
+                if (after * before < 0)
+                    continue outer;
+            }
+            fail("not enough variation in random bytes");
+        }
+    }
+
+    /**
+     * Filling an empty array with random bytes succeeds without effect.
+     */
+    public void testNextBytes_emptyArray() {
+        ThreadLocalRandom.current().nextBytes(new byte[0]);
+    }
+
+    public void testNextBytes_nullArray() {
+        try {
+            ThreadLocalRandom.current().nextBytes(null);
+            shouldThrow();
+        } catch (NullPointerException success) {}
+    }
+
 }