@Test
public void testFilter() {

    int maxLength = 2;
    IntPredicate filter = i -> i % 2 == 0;
    List<Tuple2id> result = recommender.getRecommendation(0, maxLength, filter).getIidxs();
    List<Tuple2id> expected = Arrays.asList(
            tuple(0, 6.1),
            tuple(2, 4.1)
    );
    
    assertEquals(expected, result);
}