code: def test_empty_graph(self):
      graph = layers.LayerGraph()
      self.assertEqual(len(graph), 0)
      self.assertEqual(str(graph), "[empty graph]")
  
file_path: neupy/tests/layers/graph/test_extra_features.py
imports: from neupy import layers
  from base import BaseTestCase
label_desc: Use image node_id 4 for calling the GraphExtraFeaturesTestCase obj's underlying member method code with example usage: obj.test_empty_graph() without return types