@Test
public void testAddExisted() {

    SafeIterableMap<Integer, Integer> map = from(1, 2, 3, 4).to(10, 20, 261, 40);
    assertThat(map.putIfAbsent(3, 239), is(261));
    assertThat(map, is(from(1, 2, 3, 4).to(10, 20, 261, 40)));
}