code: def test_delete_field_at_index(self):
      # test insert before index and mask
      del_sample = ner_sample.delete_field_at_index("text", [1, 3])
      self.assertEqual(
          ["EU", "call", "to", "boycott", "British", "lamb", "."],
          del_sample.dump()["x"],
      )
      self.assertEqual(
          del_sample.dump()["y"],
          ["B-ORG", "O", "O", "O", "B-MISC", "O", "O"],
      )
      self.assertEqual([0, 0, 0, 0, 0, 0, 0], del_sample.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 4 for calling the TestNERSample obj's underlying member method code with example usage: obj.test_delete_field_at_index() without return types