assertThat(set.floor("f")).isEqualTo("f");
    assertThat(set.floor("j")).isEqualTo("i");
    assertThat(set.floor("q")).isEqualTo("k");
  }

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