recs = recommender.recommend(5, -1, candidates, null);
assertThat(Lists.transform(recs, ScoredIds.idFunction()),
containsInAnyOrder(7L, 9L));
candidates.add(6);
exclude.clear();
exclude.add(9);
recs = recommender.recommend(5, -1, candidates, exclude);
assertThat(Lists.transform(recs, ScoredIds.idFunction()),
containsInAnyOrder(6L, 7L));