code: def test_add_reference_channels():
      """Test if there is a new reference channel that consist of all zeros."""
      raw = read_raw_fif(raw_fname, preload=True)
      n_raw_original_channels = len(raw.ch_names)
      epochs = Epochs(raw, read_events(eve_fname))
      epochs.load_data()
      epochs_original_shape = epochs._data.shape[1]
      evoked = epochs.average()
      n_evoked_original_channels = len(evoked.ch_names)
  
      # Raw object
      raw.add_reference_channels(["REF 123"])
      assert len(raw.ch_names) == n_raw_original_channels + 1
      assert np.all(raw.get_data()[-1] == 0)
  
      # Epochs object
      epochs.add_reference_channels(["REF 123"])
      assert epochs._data.shape[1] == epochs_original_shape + 1
  
      # Evoked object
      evoked.add_reference_channels(["REF 123"])
      assert len(evoked.ch_names) == n_evoked_original_channels + 1
      assert np.all(evoked._data[-1] == 0)
  
imports: import hashlib
  from copy import deepcopy
  from functools import partial
  from pathlib import Path
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal, assert_equal
  from scipy.io import savemat
  from mne import Epochs, EpochsArray, EvokedArray, create_info, make_ad_hoc_cov, pick_channels, pick_types, read_events
  from mne._fiff.constants import FIFF, _ch_unit_mul_named
  from mne.channels import combine_channels, equalize_channels, find_ch_adjacency, get_builtin_ch_adjacencies, make_1020_channel_selections, read_ch_adjacency, read_custom_montage, rename_channels
  from mne.channels.channels import _BUILTIN_CHANNEL_ADJACENCIES, _BuiltinChannelAdjacency, _ch_neighbor_adjacency, _compute_ch_adjacency
  from mne.datasets import testing
  from mne.io import RawArray, read_info, read_raw_bti, read_raw_ctf, read_raw_eeglab, read_raw_fif, read_raw_kit
  from mne.parallel import parallel_func
  from mne.utils import requires_good_network
label_desc: Use image node_id 15 for calling a global function with example usage: test_add_reference_channels() without return types