code: def __getitem__(self, idx):
      return self.shapes[idx]
  
file_path: mmdetection/tests/test_datasets/test_samplers/test_batch_sampler.py
imports: from unittest import TestCase
  from unittest.mock import patch
  import numpy
  from mmengine.dataset import DefaultSampler
  from torch.utils.data import Dataset
  from mmdet.datasets.samplers import AspectRatioBatchSampler
label_desc: Use image node_id 3 for calling the DummyDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: self