code: def test_custom_batch_fn(self):
      ds = DS_custom_batch_fn()
      loader = elegy.data.DataLoader(ds, batch_size=3)
      batches = list(loader)
      assert len(loader) == len(batches)
      assert batches[0]["a"].shape == (3, 10)
      assert batches[0]["b"].shape == (3,)
      assert batches[0]["c"] == "banana"
      assert np.all(batches[0]["b"] == np.array([0, 1, 2]))
  
imports: from unittest import TestCase
  import jax.numpy
  import numpy
  import optax
  import pytest
  import elegy
label_desc: Use image node_id 9 for calling the DataLoaderTestCase obj's underlying member method code with example usage: obj.test_custom_batch_fn() without return types