def METHOD_NAME(big_log, item_test_size):
    splitter = UserSplitter(
        drop_cold_items=False,
        drop_cold_users=False,
        item_test_size=item_test_size,
        seed=1234,
    )
    train, test = splitter.split(big_log)
    assert train.count() + test.count() == big_log.count()
    assert test.intersect(train).count() == 0
    if isinstance(item_test_size, int):
        #  it's a rough check. for it to be true, item_test_size must be bigger than log length for every user
        num_users = big_log.select("user_idx").distinct().count()
        assert num_users * item_test_size == test.count()
        assert big_log.count() - num_users * item_test_size == train.count()