@Test
public void shouldDuplicateElementsInAList() throws Exception {

    List<String> duplicates = P15.duplicate(Arrays.asList("a", "b", "c"), 3);
    assertThat(duplicates, hasSize(9));
    assertThat(duplicates, contains("a", "a", "a", "b", "b", "b", "c", "c", "c"));
}