code: def test_empty_html_cell(self):
      tc = new_text_cell("html")
      self.assertEqual(tc.cell_type, "html")
      self.assertEqual("source" not in tc, True)
  
imports: from __future__ import annotations
  from unittest import TestCase
  import pytest
  from nbformat.v3.nbbase import NotebookNode, nbformat, new_author, new_code_cell, new_heading_cell, new_metadata, new_notebook, new_output, new_text_cell, new_worksheet
label_desc: Use image node_id 4 for calling the TestCell obj's underlying member method code with example usage: obj.test_empty_html_cell() without return types