@Override
  public <T> T unwrap(Class<T> clazz) {
    if (clazz.isInstance(cache)) {
      return clazz.cast(cache);
    } else if (clazz.isInstance(this)) {
      return clazz.cast(this);
    }
    throw new IllegalArgumentException("Unwrapping to " + clazz
        + " is not supported by this implementation");
  }
@Test
  public void unwrap_fail() {
    assertThrows(IllegalArgumentException.class, () -> jcache.unwrap(CaffeineConfiguration.class));
  }