docstr: Empty graph
docstr_tok: ["Empty","graph"]
code: def test_trivial(self):
      """Empty graph"""
      G = nx.Graph()
      assert nx.core_number(G) == {}
  
imports: import pytest
  import networkx
  from networkx.utils import nodes_equal
label_desc: Use image node_id 2 for calling the TestCore obj's underlying member method code with example usage: obj.test_trivial() without return types