// simultaneous update for same key, some null, some non-null
    doParallelCacheOp(
        count, n -> cache.asMap().compute(key, (k, v) -> n % 2 == 0 ? v + delimiter + n : null));
    assertThat(cache.size()).isAtMost(1);
  }

  public void testCompute() {
    cache.put(key, "1");
    // simultaneous deletion
    doParallelCacheOp(count, n -> cache.asMap().compute(key, (k, v) -> null));