code: def test_ensure_string(self):
      cmd = self.cmd
      cmd.option1 = "ok"
      cmd.ensure_string("option1")
  
      cmd.option2 = None
      cmd.ensure_string("option2", "xxx")
      self.assertTrue(hasattr(cmd, "option2"))
  
      cmd.option3 = 1
      self.assertRaises(
          DistutilsOptionError, cmd.ensure_string, "option3"
      )
  
imports: import unittest
  import os
  from test.test_support import captured_stdout, run_unittest
  from distutils.cmd import Command
  from distutils.dist import Distribution
  from distutils.errors import DistutilsOptionError
  from distutils import debug
label_desc: Use image node_id 5 for calling the CommandTestCase obj's underlying member method code with example usage: obj.test_ensure_string() without return types