code: def test_kernels(metric, rndstate):
      """Test Kernels"""
      n_matrices, n_channels, n_times = 2, 5, 10
      x = rndstate.randn(n_matrices, n_channels, n_times)
      kernels = Kernels(metric=metric).fit_transform(x)
      assert kernels.shape == (n_matrices, n_channels, n_channels)
      assert is_spd(kernels)
  
imports: import numpy
  from numpy.testing import assert_array_almost_equal, assert_array_equal, assert_raises
  import pytest
  from pyriemann.estimation import Covariances, ERPCovariances, XdawnCovariances, CospCovariances, HankelCovariances, Coherences, Shrinkage, BlockCovariances, Kernels
  from pyriemann.utils.test import is_sym_pos_def, is_sym_pos_semi_def
label_desc: Use image node_id 16 for calling a global function with example usage: test_kernels(metric, rndstate) without return types