}

  private List<Entry<Object, Object>> warmUp(LoadingCache<Object, Object> cache) {
    return warmUp(cache, WARMUP_MIN, WARMUP_MAX);
  }

  /**
   * Returns the entries that were added to the map, so they won't fall out of a map with weak or
   * soft references until the caller drops the reference to the returned entries.
   */
  private List<Entry<Object, Object>> warmUp(

   * fulfills the requests (e.g., a remote server) needs "warmup" time, rather than being
   * immediately accessed at the stable (maximum) rate.
   *
   * <p>The returned {@code RateLimiter} starts in a "cold" state (i.e. the warmup period will
   * follow), and if it is left unused for long enough, it will return to that state.
   *

  }

  private List<Entry<Object, Object>> warmUp(LoadingCache<Object, Object> cache) {
    return warmUp(cache, WARMUP_MIN, WARMUP_MAX);
  }

  /**
   * Returns the entries that were added to the map, so they won't fall out of a map with weak or
   * soft references until the caller drops the reference to the returned entries.
   */
  private List<Entry<Object, Object>> warmUp(

   * fulfills the requests (e.g., a remote server) needs "warmup" time, rather than being
   * immediately accessed at the stable (maximum) rate.
   *
   * <p>The returned {@code RateLimiter} starts in a "cold" state (i.e. the warmup period will
   * follow), and if it is left unused for long enough, it will return to that state.
   *

    for (int i = 0; i < 8; i++) {
      limiter.acquire(); // // #1
    }
    stopwatch.sleepMillis(4500); // #2: back to cold state (warmup period + repay last acquire)
    for (int i = 0; i < 3; i++) { // only three steps, we're somewhere in the warmup period
      limiter.acquire(); // #3
    }

    limiter.setRate(4.0); // double the rate!

    for (int i = 0; i < 8; i++) {
      limiter.acquire(); // // #1
    }
    stopwatch.sleepMillis(4500); // #2: back to cold state (warmup period + repay last acquire)
    for (int i = 0; i < 3; i++) { // only three steps, we're somewhere in the warmup period
      limiter.acquire(); // #3
    }

    limiter.setRate(4.0); // double the rate!

          UnsupportedOperationException.class, () -> cache.asMap().keySet().addAll(asList(1, 2)));
    }
  }


  public void testKeySet_clear() {
    for (LoadingCache<Object, Object> cache : caches()) {
      warmUp(cache, 0, 100);

      Set<Object> keys = cache.asMap().keySet();
      keys.clear();
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testKeySet_empty_remove() {

          UnsupportedOperationException.class, () -> cache.asMap().keySet().addAll(asList(1, 2)));
    }
  }


  public void testKeySet_clear() {
    for (LoadingCache<Object, Object> cache : caches()) {
      warmUp(cache, 0, 100);

      Set<Object> keys = cache.asMap().keySet();
      keys.clear();
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testKeySet_empty_remove() {

    IdentityLoader<Integer> loader = identityLoader();
    LoadingCache<Integer, Integer> cache =
        CacheBuilder.newBuilder().concurrencyLevel(1).maximumSize(10).build(loader);
    CacheTesting.warmUp(cache, 0, 10);
    Set<Integer> keySet = cache.asMap().keySet();
    assertThat(keySet).containsExactly(0, 1, 2, 3, 4, 5, 6, 7, 8, 9);

    // re-order
    getAll(cache, asList(0, 1, 2));

   *          |                / .
   *          |               /  .   ← "warmup period" is the area of the trapezoid between
   *          |              /   .     thresholdPermits and maxPermits
   *          |             /    .
   *          |            /     .
   *          |           /      .
   *   stable +----------/  WARM .
   * interval |          .   UP  .
   *          |          . PERIOD.