code: def test_xgbreg_shadow_trees(precalculated_xgb_regression_explainer):
      dt = precalculated_xgb_regression_explainer.shadow_trees
      assert isinstance(dt, list)
      assert isinstance(
          dt[0], dtreeviz.models.shadow_decision_tree.ShadowDecTree
      )
  
file_path: explainerdashboard/tests/test_xgboost_treeviz.py
imports: import unittest
  import pandas
  import plotly.graph_objects
  import dtreeviz
  from xgboost import XGBClassifier
  from explainerdashboard.explainers import ClassifierExplainer
  from explainerdashboard.datasets import *
label_desc: Use image node_id 6 for calling a global function with example usage: test_xgbreg_shadow_trees(precalculated_xgb_regression_explainer) without return types