TypeWithDuplicates b1 = new TypeWithDuplicates(2, 1);
    TypeWithDuplicates b2 = new TypeWithDuplicates(2, 2);
    TypeWithDuplicates c = new TypeWithDuplicates(3, 1);
    CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableMultiset.<TypeWithDuplicates>builder().add(a).addCopies(b1, 2).add(c).build(),
            a,
            b1,
            c,
            b2);