FakeTicker ticker = new FakeTicker();
    IdentityLoader<Integer> loader = identityLoader();
    LoadingCache<Integer, Integer> cache =
        CacheBuilder.newBuilder()
            .concurrencyLevel(1)
            .expireAfterAccess(11, MILLISECONDS)
            .ticker(ticker)
            .build(loader);
    for (int i = 0; i < 10; i++) {
      cache.getUnchecked(i);
      ticker.advance(1, MILLISECONDS);

    // power of (1/concentration) and floor()ed
    max = Ints.checkedCast((long) Math.pow(distinctKeys, concentration));

    cache =
        CacheBuilder.newBuilder()
            .concurrencyLevel(segments)
            .maximumSize(maximumSize)
            .build(
                new CacheLoader<Integer, Integer>() {
                  @Override
                  public Integer load(Integer from) {

      this.expireAfterWriteNanos = expireAfterWriteNanos;
      this.expireAfterAccessNanos = expireAfterAccessNanos;
      this.maxWeight = maxWeight;
      this.weigher = weigher;
      this.concurrencyLevel = concurrencyLevel;
      this.removalListener = removalListener;
      this.ticker = (ticker == Ticker.systemTicker() || ticker == NULL_TICKER) ? null : ticker;
      this.loader = loader;
    }

       * UnsignedBytesBenchmark. TODO(cpovirk): benchmark this
       */
      /*
       * A CopyOnWriteArraySet<WeakReference> is faster than a newSetFromMap of a MapMaker map with
       * weakKeys() and concurrencyLevel(1), even up to at least 12 cached exception types.
       */
      private static final Set<WeakReference<Class<? extends Exception>>> validClasses =
          new CopyOnWriteArraySet<>();

      @Override

     * @param concurrencyLevel the estimated number of threads for concurrent updates
     * @return a new instance of {@link ConcurrentHashMap}
     * @see ConcurrentHashMap#ConcurrentHashMap(int, float, int)
     */
    public static <K, V> ConcurrentHashMap<K, V> newConcurrentHashMap(final int initialCapacity, final float loadFactor,
            final int concurrencyLevel) {

      this.expireAfterWriteNanos = expireAfterWriteNanos;
      this.expireAfterAccessNanos = expireAfterAccessNanos;
      this.maxWeight = maxWeight;
      this.weigher = weigher;
      this.concurrencyLevel = concurrencyLevel;
      this.removalListener = removalListener;
      this.ticker = (ticker == Ticker.systemTicker() || ticker == NULL_TICKER) ? null : ticker;
      this.loader = loader;
    }

  public void testReloadAfterSimulatedValueReclamation() throws ExecutionException {
    CountingLoader countingLoader = new CountingLoader();
    LoadingCache<Object, Object> cache =
        CacheBuilder.newBuilder().concurrencyLevel(1).weakValues().build(countingLoader);

    Object key = new Object();
    assertThat(cache.getUnchecked(key)).isNotNull();

    CacheTesting.simulateValueReclamation(cache, key);

  public void testReloadAfterSimulatedValueReclamation() throws ExecutionException {
    CountingLoader countingLoader = new CountingLoader();
    LoadingCache<Object, Object> cache =
        CacheBuilder.newBuilder().concurrencyLevel(1).weakValues().build(countingLoader);

    Object key = new Object();
    assertThat(cache.getUnchecked(key)).isNotNull();

    CacheTesting.simulateValueReclamation(cache, key);