code: def test_OverlayOntoBackgroundImage(self):
      self.evaluate_class(
          imaugs.OverlayOntoBackgroundImage(
              background_image=EMOJI_PATH,
              overlay_size=0.5,
              scale_bg=True,
          ),
          fname="overlay_onto_background_image",
      )
  
imports: import json
  import random
  import unittest
  from augly import image
  from augly.tests.image_tests.base_unit_test import BaseImageUnitTest
  from augly.utils import EMOJI_PATH, IMAGE_METADATA_PATH, IMG_MASK_PATH
  from PIL import Image
label_desc: Use image node_id 21 for calling the TransformsImageUnitTest obj's underlying member method code with example usage: obj.test_OverlayOntoBackgroundImage() without return types