@Test
public void shouldInsertElementAtFirstPosition_split() throws Exception {

    List<String> input = Stream.of("a", "b", "c", "d").collect(toList());
    List<String> result = P21.insertAt_split(input, 1, "alfa");
    assertThat(result, hasSize(5));
    assertThat(result, contains("alfa", "a", "b", "c", "d"));
}