assertThat(set.tailSet(strings[i], false))
          .containsExactlyElementsIn(sortedNumberNames(i + 1, strings.length))
          .inOrder();
    }
  }

  public void testFloor_emptySet() {
    ImmutableSortedSet<String> set = ImmutableSortedSet.copyOf(new String[] {});
    assertThat(set.floor("f")).isNull();
  }

  public void testFloor_elementPresent() {