code: def test_check_weights_error_positivity():
      n_matrices = 5
      w = np.ones(n_matrices)
      w[0] = 0
      with pytest.raises(ValueError):  # not strictly positive weight
          check_weights(w, n_matrices, check_positivity=True)
  
imports: import numpy
  import pytest
  from pyriemann.utils.utils import check_weights
label_desc: Use image node_id 4 for calling a global function with example usage: test_check_weights_error_positivity() without return types