code: def test_start_slice_unknown_layer(self):
      network = layers.join(
          layers.Input(10),
          layers.Relu(8),
      )
      final_layer = layers.Relu(5, name="final-relu")
  
      message = "Layer `final-relu` is not used in the graph"
      with self.assertRaisesRegexp(ValueError, message):
          network.start(final_layer)
  
file_path: neupy/tests/layers/graph/test_slicing.py
imports: import numpy
  from neupy import layers
  from neupy.utils import asfloat
  from base import BaseTestCase
label_desc: Use image node_id 12 for calling the SliceLayerConnectionsTestCase obj's underlying member method code with example usage: obj.test_start_slice_unknown_layer() without return types