code: def test_default_channel_first(self):
      im = torch.rand(4, 4)
      result = EnsureChannelFirstd("img", channel_dim="no_channel")(
          {"img": im}
      )
  
      self.assertEqual(result["img"].shape, (1, 4, 4))
  
file_path: MONAI/tests/test_ensure_channel_firstd.py
imports: from __future__ import annotations
  import os
  import tempfile
  import unittest
  import nibabel
  import numpy
  import torch
  from parameterized import parameterized
  from PIL import Image
  from monai.data.meta_tensor import MetaTensor
  from monai.transforms import EnsureChannelFirstd, LoadImaged
label_desc: Use image node_id 4 for calling the TestEnsureChannelFirstd obj's underlying member method code with example usage: obj.test_default_channel_first() without return types