Multiset<String> ms1 = HashMultiset.create(asList("a", "b", "a"));
    Multiset<String> ms2 = HashMultiset.create(asList("a", "b", "a"));
    assertEquals(ms1, union(ms1, ms2));
  }

  public void testUnionEmptyNonempty() {
    Multiset<String> ms1 = HashMultiset.create();
    Multiset<String> ms2 = HashMultiset.create(asList("a", "b", "a"));
    assertEquals(ms2, union(ms1, ms2));
  }