code: def test_insert_field_after_index(self):
      # test insert after index and mask
      ins_aft = wsc_sample.insert_field_after_index("text", 2, "$$$")
      self.assertEqual(
          "The city councilmen $$$ refused the demonstrators a permit because "
          "they feared violence.",
          ins_aft.dump()["text"],
      )
      self.assertEqual(
          ins_aft.dump()["target"],
          {
              "noun1": "The city councilmen",
              "noun2": "The demonstrators",
              "noun1_idx": 0,
              "noun2_idx": 5,
              "pron": "they",
              "pron_idx": 10,
          },
      )
  
file_path: textflint/test/input/component/sample/test_wsc_sample.py
imports: import unittest
  from textflint.input.component.sample.wsc_sample import *
label_desc: Use image node_id 4 for calling the TestWSCSample obj's underlying member method code with example usage: obj.test_insert_field_after_index() without return types