code: def test_variant_from_example(self):
      example = _mock_example_with_variant_and_alt_allele_indices()
      variant = vis.variant_from_example(example)
      self.assertIsInstance(variant, variants_pb2.Variant)
  
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 12 for calling the VisTest obj's underlying member method code with example usage: obj.test_variant_from_example() without return types