@Test
 public void assertToItemsString() {
   assertThat(ShardingItems.toItemsString(Arrays.asList(0, 1, 2)), is("0,1,2"));
 }
 @Test
 public void assertToItemsStringWhenEmpty() {
   assertThat(ShardingItems.toItemsString(Collections.<Integer>emptyList()), is(""));
 }