code: def test_pick_channels_csd():
      """Test selecting channels from a CrossSpectralDensity."""
      csd = _make_csd()
      csd = pick_channels_csd(csd, ["CH1", "CH3"])
      assert csd.ch_names == ["CH1", "CH3"]
      assert_array_equal(
          csd._data, [[0, 6, 12, 18], [2, 8, 14, 20], [5, 11, 17, 23]]
      )
  
imports: import pickle
  from itertools import product
  from os import path
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal
  from pytest import raises
  import mne
  from mne.channels import equalize_channels
  from mne.proj import Projection
  from mne.time_frequency import CrossSpectralDensity, csd_array_fourier, csd_array_morlet, csd_array_multitaper, csd_fourier, csd_morlet, csd_multitaper, csd_tfr, pick_channels_csd, read_csd, tfr_morlet
  from mne.time_frequency.csd import _sym_mat_to_vector, _vector_to_sym_mat
  from mne.utils import sum_squared
label_desc: Use image node_id 10 for calling a global function with example usage: test_pick_channels_csd() without return types