code: def test_mixture_of_experts_undefined_features(self):
      error_message = (
          "Cannot create mixture of experts model, because "
          "number of input features is unknown"
      )
      with self.assertRaisesRegexp(ValueError, error_message):
          architectures.mixture_of_experts(
              [
                  layers.Input(None) >> layers.Relu(10),
                  layers.Input(None) >> layers.Relu(10),
              ]
          )
  
file_path: neupy/tests/architectures/test_mixtures_of_experts.py
imports: import copy
  import numpy
  from sklearn import datasets, preprocessing, model_selection
  from neupy.utils import asfloat
  from neupy.exceptions import LayerConnectionError
  from neupy.algorithms.gd import objectives
  from neupy import algorithms, layers, architectures
  from base import BaseTestCase
label_desc: Use image node_id 5 for calling the MixtureOfExpertsTestCase obj's underlying member method code with example usage: obj.test_mixture_of_experts_undefined_features() without return types