code: def test_predecessor(self):
      assert nx.dfs_predecessors(self.G, source=0) == {
          1: 0,
          2: 1,
          3: 1,
          4: 2,
      }
      assert nx.dfs_predecessors(self.D) == {1: 0, 3: 2}
  
imports: import networkx
label_desc: Use image node_id 5 for calling the TestDFS obj's underlying member method code with example usage: obj.test_predecessor() without return types