@Test
public void shouldRotateWhenNIsNegative() throws Exception {

    List<String> rotated = P19.rotate(Arrays.asList("a", "b", "c", "d", "e", "f", "g", "h"), -2);
    assertThat(rotated, equalTo(Arrays.asList("g", "h", "a", "b", "c", "d", "e", "f")));
}