code: def test_prepare_covariates_insufficient_elements():
      label_df = pd.DataFrame(
          {"Trait_1": [0, -1, 1], "Trait_2": [0, 1, math.nan]}
      )
      cov_df = pd.DataFrame(
          {"Covariate_1": [0, 2], "Covariate_2": [0, -1]}
      )
      with pytest.raises(
          ValueError,
          match=r".*cov_df must be either empty of have the same number of rows as label_df.*",
      ):
          _prepare_covariates(cov_df, label_df, True)
  
imports: from glow.wgr.model_functions import *
  from glow.wgr.model_functions import _prepare_covariates, _prepare_labels_and_warn
  import math
  import numpy
  import pandas
  from pyspark.sql import Row
  import pytest
  from sklearn.linear_model import LogisticRegression
  from sklearn.datasets import load_breast_cancer
label_desc: Use image node_id 8 for calling a global function with example usage: test_prepare_covariates_insufficient_elements() without return types