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();

    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 {

      } catch (Exception e) {
        AssertionFailedError afe = new AssertionFailedError("Unexpected exception: " + e);
        afe.initCause(e);
        throw afe;
      }
    }
  }

  void checkEmpty(BlockingQueue<?> q) {
    try {
      assertTrue(q.isEmpty());
      assertEquals(0, q.size());
      assertNull(q.peek());
      assertNull(q.poll());
      assertNull(q.poll(0, MILLISECONDS));

      } catch (Exception e) {
        AssertionFailedError afe = new AssertionFailedError("Unexpected exception: " + e);
        afe.initCause(e);
        throw afe;
      }
    }
  }

  void checkEmpty(BlockingQueue<?> q) {
    try {
      assertTrue(q.isEmpty());
      assertEquals(0, q.size());
      assertNull(q.peek());
      assertNull(q.poll());
      assertNull(q.poll(0, MILLISECONDS));