code: def test_invalid_mode(self):
      with pytest.raises(KeyError):
          DecisionTreeSupervisedDiscretiserMethod(
              tree_params={"max_depth": 2}, mode="invalid"
          )
  
file_path: causalnex/tests/discretiser/test_decision_tree.py
imports: import numpy
  import pytest
  from causalnex.discretiser.discretiser_strategy import DecisionTreeSupervisedDiscretiserMethod
label_desc: Use image node_id 3 for calling the TestDecisionTree obj's underlying member method code with example usage: obj.test_invalid_mode() without return types