code: def test_plot_evoked_cov():
      """Test plot_evoked with noise_cov."""
      evoked = _get_epochs().average()
      cov = read_cov(cov_fname)
      cov["projs"] = []  # avoid warnings
      with pytest.warns(
          RuntimeWarning, match="No average EEG reference"
      ):
          evoked.plot(noise_cov=cov, time_unit="s")
      with pytest.raises(TypeError, match="Covariance"):
          evoked.plot(noise_cov=1.0, time_unit="s")
      with pytest.raises(
          FileNotFoundError, match="File does not exist"
      ):
          evoked.plot(noise_cov="nonexistent-cov.fif", time_unit="s")
      raw = read_raw_fif(raw_sss_fname)
      events = make_fixed_length_events(raw)
      epochs = Epochs(raw, events, picks=default_picks)
      cov = compute_covariance(epochs)
      evoked_sss = epochs.average()
      with pytest.warns(RuntimeWarning, match="relative scaling"):
          evoked_sss.plot(noise_cov=cov, time_unit="s")
      plt.close("all")
  
imports: from pathlib import Path
  import matplotlib.pyplot
  import numpy
  import pytest
  from matplotlib import gridspec
  from matplotlib.collections import PolyCollection
  from matplotlib.colors import same_color
  from mpl_toolkits.axes_grid1.parasite_axes import HostAxes
  from numpy.testing import assert_allclose
  import mne
  from mne import Epochs, compute_covariance, compute_proj_evoked, make_fixed_length_events, read_cov, read_events
  from mne._fiff.constants import FIFF
  from mne.datasets import testing
  from mne.io import read_raw_fif
  from mne.stats.parametric import _parametric_ci
  from mne.utils import catch_logging
  from mne.viz import plot_compare_evokeds, plot_evoked_white
  from mne.viz.utils import _fake_click, _get_cmap
label_desc: Use image node_id 3 for calling a global function with example usage: test_plot_evoked_cov() without return types