code: def test_channels_from_example(self):
      shape = (3, 2, 4)
      arr, example = _mock_example_with_image(shape)
      channels = vis.channels_from_example(example)
      self.assertLen(channels, shape[2])
      self.assertTrue((channels[0] == arr[:, :, 0]).all())
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import glob
  import os
  from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from third_party.nucleus.protos import variants_pb2
  from third_party.nucleus.testing import test_utils
  from third_party.nucleus.util import vis
  from tensorflow.core.example import example_pb2
  from tensorflow.core.example import feature_pb2
label_desc: Use image node_id 3 for calling the VisTest obj's underlying member method code with example usage: obj.test_channels_from_example() without return types