code: def test_reverse_substitute_snippet(self):
      snippet = "the patient is in the emergency room."
      index_to_pair = {
          4: ("pt", "patient"),
          22: ("er", "emergency room"),
      }
      result = c4_wsrs_utils._reverse_substitute_snippet(
          snippet, index_to_pair, substitution_rate=1.0
      )
      self.assertEqual(result, "the pt is in the er.")
  
file_path: datasets/tensorflow_datasets/text/c4_wsrs/c4_wsrs_utils_test.py
imports: import re
  from unittest import mock
  from absl.testing import absltest
  import numpy
  from tensorflow_datasets.text.c4_wsrs import c4_wsrs_utils
label_desc: Use image node_id 4 for calling the C4WsrsUtilsTest obj's underlying member method code with example usage: obj.test_reverse_substitute_snippet() without return types