code: def test_load_png(self):
      spatial_size = (6, 6, 3)
      test_image = np.random.randint(0, 6, size=spatial_size)
      with tempfile.TemporaryDirectory() as tempdir:
          filename = os.path.join(tempdir, "test_image.png")
          Image.fromarray(test_image.astype("uint8")).save(filename)
          result = LoadImage(image_only=True)(filename)
          result = EnsureChannelFirst()(result)
          self.assertEqual(result.shape[0], 3)
          result = EnsureChannelFirst(channel_dim=-1)(result)
          self.assertEqual(result.shape, (6, 3, 6))
  
file_path: MONAI/tests/test_ensure_channel_first.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 EnsureChannelFirst, LoadImage
  from monai.utils import optional_import
label_desc: Use image node_id 3 for calling the TestEnsureChannelFirst obj's underlying member method code with example usage: obj.test_load_png() without return types