@Override
                  protected Set<String> create(String[] elements) {
                    Set<String> set = newHashSet(elements);
                    Set<String> other = newHashSet("wz", "xq");
                    set.addAll(other);
                    other.add("pq");
                    return Sets.difference(set, other);
                  }
                })
            .named("set - set")

                  @Override
                  protected Set<String> create(String[] elements) {
                    Set<String> set = newHashSet(elements);
                    Set<String> other = newHashSet("wz", "xq");
                    set.addAll(other);
                    other.add("pq");
                    return Sets.difference(set, other);
                  }
                })
            .named("set - set")