code: def test_density(self):
      assert nx.density(self.G) == 0.5
      assert nx.density(self.DG) == 0.3
      G = nx.Graph()
      G.add_node(1)
      assert nx.density(G) == 0.0
  
imports: import random
  import pytest
  import networkx
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 16 for calling the TestFunction obj's underlying member method code with example usage: obj.test_density() without return types