for (LoadingCache<Object, Object> cache : caches()) {
      checkEmpty(cache);
    }
  }


  public void testInvalidate_empty() {
    for (LoadingCache<Object, Object> cache : caches()) {
      cache.getUnchecked("a");
      cache.getUnchecked("b");
      cache.invalidate("a");
      cache.invalidate("b");
      cache.invalidate(0);
      checkEmpty(cache);
    }
  }

  public void testInvalidateAll_empty() {

        assertTrue(keys.contains(key));
        assertTrue(keys.remove(key));
        assertFalse(keys.remove(key));
        assertFalse(keys.contains(key));
      }
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testValues_populated() {
    for (LoadingCache<Object, Object> cache : caches()) {
      Collection<Object> values = cache.asMap().values();

        assertTrue(keys.contains(key));
        assertTrue(keys.remove(key));
        assertFalse(keys.remove(key));
        assertFalse(keys.contains(key));
      }
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testValues_populated() {
    for (LoadingCache<Object, Object> cache : caches()) {
      Collection<Object> values = cache.asMap().values();

    }
  }

  public void testEmpty() throws Exception {
    for (BlockingQueue<Object> q : blockingQueues()) {
      checkEmpty(q);
    }
  }

  private void checkEmpty(BlockingQueue<Object> q) {
    assertDrained(q);
  }

  public void testNegativeMaxElements() throws Exception {
    for (BlockingQueue<Object> q : blockingQueues()) {

    assertEquals(0, nullCache.size());
    Object key = new Object();
    assertSame(key, nullCache.getUnchecked(key));
    assertEquals(1, listener.getCount());
    assertEquals(0, nullCache.size());
    CacheTesting.checkEmpty(nullCache.asMap());
  }

  @GwtIncompatible // QueuingRemovalListener
  public void testRemovalNotification_clear() throws InterruptedException {

    assertEquals(0, nullCache.size());
    Object key = new Object();
    assertSame(key, nullCache.getUnchecked(key));
    assertEquals(1, listener.getCount());
    assertEquals(0, nullCache.size());
    CacheTesting.checkEmpty(nullCache.asMap());
  }

  @GwtIncompatible // QueuingRemovalListener
  public void testRemovalNotification_clear() throws InterruptedException {