code: def test_if_layer_in_the_graph(self):
      network = layers.join(
          layers.Input(10),
          layers.Relu(2),
      )
      final_layer = layers.Sigmoid(1)
      self.assertNotIn(final_layer, network)
  
      network_2 = layers.join(network, final_layer)
      self.assertIn(final_layer, network_2)
  
file_path: neupy/tests/layers/graph/test_usage.py
imports: import numpy
  from neupy import layers
  from neupy.utils import asfloat
  from base import BaseTestCase
label_desc: Use image node_id 6 for calling the UsageTestCase obj's underlying member method code with example usage: obj.test_if_layer_in_the_graph() without return types