docstr: Verify that an empty directed graph results in no compressor nodes
docstr_tok: ["Verify","that","an","empty","directed","graph","results","in","no","compressor","nodes"]
code: def test_empty(self):
      """
      Verify that an empty directed graph results in no compressor nodes
      """
      G = nx.DiGraph()
      compressed_graph, c_nodes = nx.dedensify(G, threshold=2)
      assert c_nodes == set()
  
imports: import pytest
  import networkx
label_desc: Use image node_id 3 for calling the TestDirectedDedensification obj's underlying member method code with example usage: obj.test_empty() without return types