code: def ensure_newline(self, n):
          
          assert n >= 0
          text = self._output.getvalue().rstrip('\n')
          if not text:
              return
          self._output = StringIO()
          self._output.write(text)
          self._output.write('\n' * n)
          text = self._output.getvalue()
          assert text[-n-1] != '\n'
          assert text[-n:] == '\n' * n
docs: Make sure there are 'n' line breaks at the end.