code: def test_potato_partial_fit_not_fitted(get_mats):
      n_matrices, n_channels = 6, 3
      covmats = get_mats(n_matrices, n_channels, "spd")
      with pytest.raises(ValueError):  # potato not fitted
          Potato().partial_fit(covmats)
  
imports: from conftest import get_metrics
  import numpy
  from numpy.testing import assert_array_equal
  import pytest
  from pyriemann.clustering import Kmeans, KmeansPerClassTransform, Potato, PotatoField
label_desc: Use image node_id 4 for calling a global function with example usage: test_potato_partial_fit_not_fitted(get_mats) without return types