code: def test_functions_error():
      n_matrices, n_dim = 3, 4
      mean, sigma = np.eye(n_dim), 2.0
      with pytest.raises(ValueError):  # mean is not a matrix
          sample_gaussian_spd(n_matrices, np.ones(n_dim), sigma)
      with pytest.raises(ValueError):  # sigma is not a scalar
          sample_gaussian_spd(n_matrices, mean, np.ones(n_dim))
      with pytest.raises(ValueError):  # n_matrices is negative
          sample_gaussian_spd(-n_matrices, mean, sigma)
      with pytest.raises(ValueError):  # n_matrices is not an integer
          sample_gaussian_spd(4.2, mean, sigma)
      with pytest.raises(ValueError):  # n_dim is not an integer
          generate_random_spd_matrix(1.7)
      with pytest.raises(ValueError):  # n_dim is negative
          generate_random_spd_matrix(-n_dim)
  
file_path: pyRiemann/tests/test_sampling.py
imports: import pytest
  import numpy
  from pyriemann.datasets.sampling import sample_gaussian_spd, generate_random_spd_matrix
  from pyriemann.utils.distance import distance_riemann
  from pyriemann.utils.test import is_sym_pos_def
label_desc: Use image node_id 6 for calling a global function with example usage: test_functions_error() without return types