code: def test_pick_channels_mixin():
      """Test channel-picking functionality."""
      evoked = read_evokeds(fname, condition=0, proj=True)
      ch_names = evoked.ch_names[:3]
  
      ch_names_orig = evoked.ch_names
      dummy = evoked.copy().pick(ch_names)
      assert_equal(ch_names, dummy.ch_names)
      assert_equal(ch_names_orig, evoked.ch_names)
      assert_equal(len(ch_names_orig), len(evoked.data))
  
      evoked.pick(ch_names)
      assert_equal(ch_names, evoked.ch_names)
      assert_equal(len(ch_names), len(evoked.data))
  
      evoked = read_evokeds(fname, condition=0, proj=True)
      assert "meg" in evoked
      assert "eeg" in evoked
      evoked.pick(picks="eeg")
      assert "meg" not in evoked
      assert "eeg" in evoked
      assert len(evoked.ch_names) == 60
  
imports: import pickle
  from copy import deepcopy
  from pathlib import Path
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_almost_equal, assert_array_equal, assert_equal
  from scipy import fftpack
  from mne import Epochs, EpochsArray, combine_evoked, create_info, equalize_channels, pick_types, read_events, read_evokeds, write_evokeds
  from mne._fiff.constants import FIFF
  from mne.evoked import Evoked, EvokedArray, _get_peak
  from mne.io import read_raw_fif
  from mne.utils import grand_average
label_desc: Use image node_id 19 for calling a global function with example usage: test_pick_channels_mixin() without return types