@Override
  public boolean isEmpty() {
    reap();
    return backingStore.isEmpty();
  }
@Test
  void stressMap() {

    for (int i = 1; i <= TEST_SIZE; i++) {
      data.add("Data_" + i);
    }

    List<Thread> threads = new ArrayList<>(80);
    for (int i = 0; i <= 80; i++) {
      final int seed = (i + 1) * 100;
      Runnable runnable = () -> rundata(seed);
      Thread t = new Thread(runnable);
      threads.add(t);
    }
    threads.forEach(Thread::start);
    threads.forEach((Thread t) -> {
      try {
        t.join();
      } catch (InterruptedException e) {
        throw new RuntimeException(e);
      }
    });
    Assertions.assertTrue(exceptions.isEmpty());
  }