CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableSortedSet.of("a", "b", "c", "d"), "a", "b", "a", "c", "b", "b", "d");
  }

  public void testToImmutableSortedSet_customComparator() {
    Collector<String, ?, ImmutableSortedSet<String>> collector =
        toImmutableSortedSet(String.CASE_INSENSITIVE_ORDER);