CacheBuilder<Object, Object> builder = CacheBuilder.newBuilder().removalListener(testListener);
    assertThrows(IllegalStateException.class, () -> builder.removalListener(testListener));
  }

  public void testValuesIsNotASet() {
    assertThat(CacheBuilder.newBuilder().build().asMap().values() instanceof Set).isFalse();
  }

  @GwtIncompatible // CacheTesting
  public void testNullCache() {