assertTrue(initialSize == 1 || initialSize == 2);

    // wait up to 5s
    byte[] filler = new byte[1024];
    for (int i = 0; i < 500; i++) {
      System.gc();

      CacheTesting.drainReferenceQueues(cache);
      if (cache.size() == 1) {
        break;
      }
      try {
        Thread.sleep(10);
      } catch (InterruptedException e) {
        /* ignore */
      }
      try {

      if (tryLock()) {
        try {
          drainReferenceQueues();
        } finally {
          unlock();
        }
      }
    }

    /**
     * Drain the key and value reference queues, cleaning up internal entries containing garbage
     * collected keys or values.
     */
    @GuardedBy("this")
    void drainReferenceQueues() {
      if (map.usesKeyReferences()) {