@Override
  public Object[] toArray() {
    return mElements;
  }
@Test
  public void toArray() {
    String[] array = new String[]{"a", "b", "c", "d"};
    UnmodifiableArrayList<String> list = new UnmodifiableArrayList<>(array);
    assertArrayEquals(array, list.toArray());

    array[0] = "c";
    assertArrayEquals(array, list.toArray());
  }