code: def assert_fitted(oz):
      for field in LEARNED_FIELDS:
          assert hasattr(oz, field)
  
file_path: yellowbrick/tests/test_regressor/test_influence.py
imports: import pytest
  import numpy
  import matplotlib.pyplot
  from tests.base import VisualTestCase
  from tests.fixtures import Dataset
  from sklearn.datasets import make_regression
  from yellowbrick.regressor.influence import *
  from yellowbrick.datasets import load_concrete
label_desc: Use image node_id 3 for calling a global function with example usage: assert_fitted(oz) without return types