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()) {
      checkDrainThrows(q);
    }
  }

  private void checkDrainThrows(BlockingQueue<Object> q) {