code: def _generate_data(num_vars):
      return (
          np.random.normal(0, 1, (1000, num_vars)),
          np.random.choice(20, num_vars) - 10,
      )
  
imports: import random
  import numpy
  import pytest
  from flaky import flaky
  from pytest import approx
  from dowhy.gcm.shapley import ShapleyApproximationMethods, ShapleyConfig, estimate_shapley_values
  from dowhy.gcm.stats import permute_features
  from dowhy.gcm.util.general import means_difference
label_desc: Use image node_id 12 for calling a global function with example usage: _generate_data(num_vars) and returns: np,  unknown