code: def testValidDataFormatChannelsLast(self, data_format):
      test = group_norm.GroupNorm(
          groups=5,
          data_format=data_format,
          create_scale=False,
          create_offset=False,
      )
  
      self.assertEqual(test._channel_index, -1)
  
imports: from absl.testing import parameterized
  import numpy
  from sonnet.src import group_norm
  from sonnet.src import initializers
  from sonnet.src import test_utils
  import tensorflow
label_desc: Use image node_id 10 for calling the GroupNormTest obj's underlying member method code with example usage: obj.testValidDataFormatChannelsLast(data_format) without return types