code: def test_group_norm_weight_init_exception(self):
      network = layers.join(
          layers.Input((10, 10, None)),
          layers.GroupNorm(4),
      )
  
      message = (
          "Cannot initialize variables when number of "
          "channels is unknown."
      )
      with self.assertRaisesRegexp(WeightInitializationError, message):
          network.create_variables()
  
      with self.assertRaisesRegexp(WeightInitializationError, message):
          network.outputs
  
imports: import tempfile
  import numpy
  import tensorflow
  from scipy import stats
  from neupy import layers, algorithms, storage
  from neupy.utils import asfloat
  from neupy.exceptions import LayerConnectionError, WeightInitializationError
  from base import BaseTestCase
  from helpers import simple_classification
label_desc: Use image node_id 3 for calling the GroupNormTestCase obj's underlying member method code with example usage: obj.test_group_norm_weight_init_exception() without return types