text: import os
  import pytest
  import time
  
  # selenium test version for 'prompt_numbers.js' 
  
  def get_prompt(nb, index):
      cell = nb.cells[0]
      return cell.find_element_by_class_name('input').find_element_by_class_name('input_prompt').get_attribute('innerHTML').strip() 
  
  def set_prompt(nb, index, value):
      nb.set_cell_input_prompt(index, value)
  
  def test_prompt_numbers(notebook):
      cell_index = 0
      a = 'print("a")'
      notebook.edit_cell(index=cell_index, content=a)
      assert get_prompt(notebook, cell_index) == "<bdi>In</bdi>&nbsp;[&nbsp;]:"
      set_prompt(notebook, cell_index, 2);
      assert get_prompt(notebook, cell_index) == "<bdi>In</bdi>&nbsp;[2]:"
      set_prompt(notebook, cell_index, 0);
      assert get_prompt(notebook, cell_index) == "<bdi>In</bdi>&nbsp;[0]:"
      set_prompt(notebook, cell_index, "'*'");
      assert get_prompt(notebook, cell_index) == "<bdi>In</bdi>&nbsp;[*]:"
      set_prompt(notebook, cell_index, "undefined");
      assert get_prompt(notebook, cell_index) == "<bdi>In</bdi>&nbsp;[&nbsp;]:"
      set_prompt(notebook, cell_index, "null");
      assert get_prompt(notebook, cell_index) == "<bdi>In</bdi>&nbsp;[&nbsp;]:"
  