class_docstr: Test the DiGraph structure we use to represent dependencies in PackageExporter
code: def test_successors(self):
      g = DiGraph()
      g.add_edge("foo", "bar")
      g.add_edge("foo", "baz")
      g.add_node("qux")
  
      self.assertIn("bar", list(g.successors("foo")))
      self.assertIn("baz", list(g.successors("foo")))
      self.assertEqual(len(list(g.successors("qux"))), 0)
  
file_path: pytorch/test/package/test_digraph.py
imports: from torch.package._digraph import DiGraph
  from torch.testing._internal.common_utils import run_tests
label_desc: Use image node_id 1 for calling the TestDiGraph obj's underlying member method code with example usage: obj.test_successors() without return types