@Test
 public void sumUsingRecursion() {
   assertThat(arrayOperations.sumUsingRecursion(null), is(0));
   assertThat(arrayOperations.sumUsingRecursion(new int[] {}), is(0));
   assertThat(arrayOperations.sumUsingRecursion(new int[] {1}), is(1));
   assertThat(arrayOperations.sumUsingRecursion(new int[] {1, 4, 5, 8}), is(18));
 }