code: def test_density_selfloop(self):
      G = nx.Graph()
      G.add_edge(1, 1)
      assert nx.density(G) == 0.0
      G.add_edge(1, 2)
      assert nx.density(G) == 2.0
  
imports: import random
  import pytest
  import networkx
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 17 for calling the TestFunction obj's underlying member method code with example usage: obj.test_density_selfloop() without return types