code: def test_svd_predict_bad_user():
      algo = svd.BiasedSVD(2)
      algo.fit(simple_df)
  
      preds = algo.predict_for_user(50, [3])
      assert len(preds) == 1
      assert preds.index[0] == 3
      assert np.isnan(preds.loc[3])
  
file_path: lkpy/tests/test_svd.py
imports: import logging
  import pickle
  from lenskit.algorithms import svd
  import pandas
  import numpy
  from pytest import approx, mark
  import lenskit.util.test
  from lenskit.util import clone
label_desc: Use image node_id 4 for calling a global function with example usage: test_svd_predict_bad_user() without return types