code: def test_bias_global_only():
      algo = Bias(users=False, items=False)
      algo.fit(simple_df)
      assert algo.mean_ == approx(3.5)
      assert algo.item_offsets_ is None
      assert algo.user_offsets_ is None
  
imports: from lenskit.algorithms.bias import Bias
  from lenskit import util
  import logging
  import pickle
  import binpickle
  import pandas
  import numpy
  from pytest import approx, raises, mark
  from lenskit.util.test import ml_test
label_desc: Use image node_id 4 for calling a global function with example usage: test_bias_global_only() without return types