@Test
public void testContains() {

    FastSafeIterableMap<Integer, Integer> map = new FastSafeIterableMap<>();
    map.putIfAbsent(10, 20);
    map.putIfAbsent(20, 40);
    map.putIfAbsent(30, 60);
    assertThat(map.contains(10), is(true));
    assertThat(map.contains(11), is(false));
    assertThat(new FastSafeIterableMap<Integer, Integer>().contains(0), is(false));
}