code: def test_eta_decay(self, tree_method: str) -> None:
      self.run_eta_decay(tree_method)
  
imports: import json
  import os
  import tempfile
  from typing import Union
  import pytest
  import xgboost
  from xgboost import testing
label_desc: Use image node_id 13 for calling the TestCallbacks obj's underlying member method code with example usage: obj.test_eta_decay(tree_method) without return types