// explicitly remove the existing value
    cache.asMap().computeIfPresent(1, (key, value) -> null);
    assertThat(notifications).hasSize(1);
    CacheTesting.checkEmpty(cache);

    // ensure no zombie entry remains
    cache.asMap().computeIfPresent(1, (key, value) -> null);
    assertThat(notifications).hasSize(1);
    CacheTesting.checkEmpty(cache);
  }

  public void testUpdates() {