code: def test_absent_source(self, fn):
      G = nx.path_graph(2)
      with pytest.raises(nx.NodeNotFound):
          fn(G, 3, 0)
      # Test when source == target, which is handled specially by some functions
      with pytest.raises(nx.NodeNotFound):
          fn(G, 3, 3)
  
imports: import pytest
  import networkx
  from networkx.utils import pairwise
label_desc: Use image node_id 5 for calling the TestWeightedPath obj's underlying member method code with example usage: obj.test_absent_source(fn) without return types