assertThat(set.headSet("g")).containsExactly("b", "c", "d", "e", "f").inOrder();
    assertSame(this.<String>of(), set.headSet("a"));
    assertSame(this.<String>of(), set.headSet("b"));
  }

  public void testOf_tailSet() {
    SortedSet<String> set = of("e", "f", "b", "d", "c");
    assertTrue(set.tailSet("e") instanceof ImmutableSortedSet);
    assertThat(set.tailSet("e")).containsExactly("e", "f").inOrder();