@Test
public void testPut() {

    FastSafeIterableMap<Integer, Integer> map = new FastSafeIterableMap<>();
    map.putIfAbsent(10, 20);
    map.putIfAbsent(20, 40);
    map.putIfAbsent(30, 60);
    assertThat(map.putIfAbsent(5, 10), is((Integer) null));
    assertThat(map.putIfAbsent(10, 30), is(20));
}