docstr: Test undirected edge between treatment and outcome.
docstr_tok: ["Test","undirected","edge","between","treatment","and","outcome","."]
code: def test_2(self):
      """
      Test undirected edge between treatment and outcome.
      """
      # Since undirected graph, identify effect must throw an error.
      with pytest.raises(Exception):
          identified_estimand = identify_effect_id(
              build_graph_from_str("digraph{T->Y; Y->T;}"),
              action_nodes=["T"],
              outcome_nodes=["Y"],
          )
  
file_path: dowhy/tests/causal_identifiers/test_id_identifier.py
imports: import pytest
  from dowhy import identify_effect_id
  from dowhy.graph import build_graph_from_str
label_desc: Use image node_id 2 for calling the TestIDIdentifier obj's underlying member method code with example usage: obj.test_2() without return types