code: def test_string(self):
      X = np.array([["a", "b"], ["c", "d"]])
      with self.assertRaises(ValueError):
          CategoryShift().fit_transform(X)
  
file_path: auto-sklearn/test/test_pipeline/implementations/test_CategoryShift.py
imports: import numpy
  import scipy.sparse
  from autosklearn.pipeline.implementations.CategoryShift import CategoryShift
  import unittest
label_desc: Use image node_id 4 for calling the CategoryShiftTest obj's underlying member method code with example usage: obj.test_string() without return types