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

  public void testToImmutableSortedSet_duplicates() {
    class TypeWithDuplicates implements Comparable<TypeWithDuplicates> {
      final int a;
      final int b;

      TypeWithDuplicates(int a, int b) {
        this.a = a;
        this.b = b;