@Test
public void testPut() {

    SafeIterableMap<Integer, Integer> map = from(1, 2, 3, 4).to(10, 20, 30, 40);
    assertThat(map.putIfAbsent(5, 10), is((Integer) null));
    assertThat(map, is(from(1, 2, 3, 4, 5).to(10, 20, 30, 40, 10)));
}