code: def test_not_permissible_type(self, graph):
      schema = {
          0: "unknown data type",
      }
      with pytest.raises(ValueError, match="Unknown data type"):
          _ = sem_generator(
              graph=graph,
              schema=schema,
              default_type="continuous",
              noise_std=1.0,
              n_samples=1000,
              intercept=False,
              seed=12,
          )
  
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 3 for calling the TestMixedDataGen obj's underlying member method code with example usage: obj.test_not_permissible_type(graph) without return types