ImmutableSortedSet<String> set =
        ImmutableSortedSet.copyOf(new String[] {"e", "e", "f", "b", "i", "d", "c", "k"});
    assertThat(set.floor("a")).isNull();
  }

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

  public void testCeiling_elementPresent() {