List<Object> buf = new ArrayList<>();
    int elements = Queues.drain(q, buf, -1, MAX_VALUE, NANOSECONDS);
    assertEquals(0, elements);
    assertThat(buf).isEmpty();

    // Free the producer thread, and give subsequent tests a clean slate.
    q.take();
  }

  public void testDrain_throws() throws Exception {
    for (BlockingQueue<Object> q : blockingQueues()) {

  }

  void checkEmpty(BlockingQueue<?> q) {
    try {
      assertTrue(q.isEmpty());
      assertEquals(0, q.size());
      assertThat(q.peek()).isNull();
      assertThat(q.poll()).isNull();
      assertThat(q.poll(0, MILLISECONDS)).isNull();
      assertEquals("[]", q.toString());
      assertThat(q.toArray()).isEmpty();
      assertFalse(q.iterator().hasNext());
      try {
        q.element();

    return keyOrNull(higherEntry(key));
  }

  @Override
  public @Nullable Entry<K, V> firstEntry() {
    return isEmpty() ? null : entrySet().asList().get(0);
  }

  @Override
  public @Nullable Entry<K, V> lastEntry() {
    return isEmpty() ? null : entrySet().asList().get(size() - 1);
  }

  /**
   * Guaranteed to throw an exception and leave the map unmodified.
   *

      }
    },
    ArrayTableImpl {
      @Override
      <R extends Comparable<R>, C extends Comparable<C>, V> Table<R, C, V> create(
          Table<R, C, V> contents) {
        if (contents.isEmpty()) {
          return ImmutableTable.of();
        } else {
          return ArrayTable.create(contents);
        }
      }
    },
    ImmutableTableImpl {
      @Override

      }
    }

    void execute() {
      synchronized (runnables) {
        if (executed) {
          return;
        }
        executed = true;
      }

      while (!runnables.isEmpty()) {
        runnables.poll().execute();
      }
    }

    private static class RunnableExecutorPair {
      final Runnable runnable;
      final Executor executor;

   */
  @Override
  public void close() throws IOException {
    Throwable throwable = thrown;

    // close closeables in LIFO order
    while (!stack.isEmpty()) {
      Closeable closeable = stack.removeFirst();
      try {
        closeable.close();
      } catch (Throwable e) {
        if (throwable == null) {
          throwable = e;
        } else {

 * {@snippet :
 * final WeakHashMap<Object, Object> map = new WeakHashMap<>();
 * map.put(new Object(), Boolean.TRUE);
 * GcFinalization.awaitDone(new FinalizationPredicate() {
 *   public boolean isDone() {
 *     return map.isEmpty();
 *   }
 * });
 * }
 *
 * <p>Even if your non-test code does not use finalization, you can use this class to test for
 * leaks, by ensuring that objects are no longer strongly referenced:
 *
 * {@snippet :

    assertThat(subset).containsExactly("b", "c", "d", "e").inOrder();

    subset.clear();
    assertThat(elementSet).containsExactly("a", "f").inOrder();
    assertThat(subset).isEmpty();
    assertEquals(3, ms.size());
  }

  public void testCustomComparator() throws Exception {
    Comparator<String> comparator =
        new Comparator<String>() {
          @Override

      }
    } else {
      keys[dstIndex] = null;
      values[dstIndex] = null;
      entries[dstIndex] = 0;
    }
  }

  int firstEntryIndex() {
    return isEmpty() ? -1 : 0;
  }

  int getSuccessor(int entryIndex) {
    return (entryIndex + 1 < size) ? entryIndex + 1 : -1;
  }

  /**

    // TODO(kevinb): Support a concurrently modified collection?
    Iterable<E> iterable = getDelegate();
    if (iterable instanceof List) {
      List<E> list = (List<E>) iterable;
      if (list.isEmpty()) {
        return Optional.absent();
      }
      return Optional.of(list.get(list.size() - 1));
    }
    Iterator<E> iterator = iterable.iterator();
    if (!iterator.hasNext()) {