assertSame(set, copy);
  }

  public void testSingle_comparator() {
    SortedSet<String> set = of("e");
    assertSame(Ordering.natural(), set.comparator());
  }

  public void testSingle_headSet() {
    SortedSet<String> set = of("e");
    assertTrue(set.headSet("g") instanceof ImmutableSortedSet);
    assertThat(set.headSet("g")).contains("e");
    assertSame(this.<String>of(), set.headSet("c"));