code: def test_insert_field_after_index(self):
      # test insert before index and mask
      ins_aft = ner_sample.insert_field_after_index("text", 2, "$$$")
      self.assertEqual(
          [
              "EU",
              "rejects",
              "German",
              "$$$",
              "call",
              "to",
              "boycott",
              "British",
              "lamb",
              ".",
          ],
          ins_aft.dump()["x"],
      )
      self.assertEqual(
          ins_aft.dump()["y"],
          [
              "B-ORG",
              "O",
              "B-MISC",
              "O",
              "O",
              "O",
              "O",
              "B-MISC",
              "O",
              "O",
          ],
      )
      self.assertEqual(
          [0, 0, 0, 2, 0, 0, 0, 0, 0, 0], ins_aft.text.mask
      )
  
file_path: textflint/test/input/component/sample/test_ner_sample.py
imports: import unittest
  from textflint.input.component.sample.ner_sample import *
label_desc: Use image node_id 3 for calling the TestNERSample obj's underlying member method code with example usage: obj.test_insert_field_after_index() without return types