code: def test_pil_to_str(self):
      image_str = image_utils.convert_pil_to_image_str(_TEST_IMAGE_RGB)
      self.assertIsNotNone(image_str)
  
file_path: lit/lit_nlp/lib/image_utils_test.py
imports: from absl.testing import absltest
  from absl.testing import parameterized
  from lit_nlp.lib import image_utils
  import numpy
  from PIL import Image
label_desc: Use image node_id 1 for calling the ImageUtilsTest obj's underlying member method code with example usage: obj.test_pil_to_str() without return types