code: def test_scan_mode_checked(self):
      with self.assertRaises(Exception):
          ot_distance(pd.Series(), pd.Series(), mode="Wrong")
  
imports: import numpy
  import pandas
  from aif360.metrics.ot_metric import _normalize, _transform, _evaluate
  from aif360.sklearn.metrics import ot_distance
  from ot import emd2
  import unittest
  from unittest import TestCase
label_desc: Use image node_id 2 for calling the TestOtBiasScan obj's underlying member method code with example usage: obj.test_scan_mode_checked() without return types