code: def test_potato_partial_fit_no_poslabel(get_mats, get_labels):
      n_matrices, n_channels, n_classes = 6, 3, 2
      covmats = get_mats(n_matrices, n_channels, "spd")
      labels = get_labels(n_matrices, n_classes)
      pt = Potato().fit(covmats, labels)
      with pytest.raises(ValueError):  # no positive labels
          pt.partial_fit(covmats, [0] * n_matrices)
  
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 6 for calling a global function with example usage: test_potato_partial_fit_no_poslabel(get_mats, get_labels) without return types