code: def _init_test_defaultbox_generator(self):
      aspect_ratios = [[2]]
      dbox_generator = DefaultBoxGenerator(aspect_ratios)
  
      return dbox_generator
  
file_path: vision/test/test_models_detection_anchor_utils.py
imports: import pytest
  import torch
  from common_utils import assert_equal
  from torchvision.models.detection.anchor_utils import AnchorGenerator, DefaultBoxGenerator
  from torchvision.models.detection.image_list import ImageList
label_desc: Use image node_id 3 for calling the Tester obj's underlying member method code with example usage: obj._init_test_defaultbox_generator() and returns: dbox_generator