code: def test_graph_not_a_dag(self):
      graph = StructureModel()
      graph.add_edges_from([(0, 1), (1, 2), (2, 0)])
  
      with pytest.raises(
          ValueError, match="Provided graph is not a DAG"
      ):
          _ = sem_generator(graph=graph, seed=42)
  
imports: import operator
  from typing import Hashable, Tuple, Union
  import networkx
  import numpy
  import pandas
  import pytest
  from networkx.algorithms.dag import is_directed_acyclic_graph
  from sklearn.gaussian_process.kernels import RBF
  from causalnex.structure.data_generators.core import _sample_binary_from_latent, _sample_count_from_latent, _sample_poisson, generate_structure, nonlinear_sem_generator, sem_generator
  from causalnex.structure.structuremodel import StructureModel
label_desc: Use image node_id 2 for calling the TestMixedDataGen obj's underlying member method code with example usage: obj.test_graph_not_a_dag() without return types