code: def test_mean_power_errors(get_mats):
      """Test the power mean errors"""
      n_matrices, n_channels = 3, 2
      mats = get_mats(n_matrices, n_channels, "spd")
  
      with pytest.raises(ValueError):  # exponent is not a scalar
          mean_power(mats, [1])
      with pytest.raises(ValueError):  # exponent is not in [-1,1]
          mean_power(mats, 3)
  
imports: import numpy
  from scipy.stats import gmean
  import pytest
  from pytest import approx
  from pyriemann.utils.geodesic import geodesic_riemann
  from pyriemann.utils.mean import mean_covariance, mean_ale, mean_alm, mean_euclid, mean_harmonic, mean_identity, mean_kullback_sym, mean_logdet, mean_logeuclid, mean_power, mean_riemann, mean_wasserstein, maskedmean_riemann, nanmean_riemann
label_desc: Use image node_id 12 for calling a global function with example usage: test_mean_power_errors(get_mats) without return types