code: def test_plot_filter():
      """Test filter plotting."""
      l_freq, h_freq, sfreq = 2.0, 40.0, 1000.0
      data = np.zeros(5000)
      freq = [0, 2, 40, 50, 500]
      gain = [0, 1, 1, 0, 0]
      h = create_filter(
          data, sfreq, l_freq, h_freq, fir_design="firwin2"
      )
      plot_filter(h, sfreq)
      plt.close("all")
      plot_filter(h, sfreq, freq, gain)
      plt.close("all")
      iir = create_filter(data, sfreq, l_freq, h_freq, method="iir")
      plot_filter(iir, sfreq)
      plt.close("all")
      iir = create_filter(
          data,
          sfreq,
          l_freq,
          h_freq,
          method="iir",
          iir_params={"output": "ba"},
      )
      plot_filter(iir, sfreq, compensate=True)
      plt.close("all")
      iir = create_filter(
          data,
          sfreq,
          l_freq,
          h_freq,
          method="iir",
          iir_params={"output": "sos"},
      )
      plot_filter(iir, sfreq, compensate=True)
      plt.close("all")
      plot_filter(iir, sfreq, freq, gain)
      plt.close("all")
      iir_ba = create_filter(
          data,
          sfreq,
          l_freq,
          h_freq,
          method="iir",
          iir_params=dict(output="ba"),
      )
      plot_filter(iir_ba, sfreq, freq, gain)
      plt.close("all")
      fig = plot_filter(h, sfreq, freq, gain, fscale="linear")
      assert len(fig.axes) == 3
      plt.close("all")
      fig = plot_filter(
          h, sfreq, freq, gain, fscale="linear", plot=("time", "delay")
      )
      assert len(fig.axes) == 2
      plt.close("all")
      fig = plot_filter(
          h,
          sfreq,
          freq,
          gain,
          fscale="linear",
          plot=["magnitude", "delay"],
      )
      assert len(fig.axes) == 2
      plt.close("all")
      fig = plot_filter(
          h, sfreq, freq, gain, fscale="linear", plot="magnitude"
      )
      assert len(fig.axes) == 1
      plt.close("all")
      fig = plot_filter(
          h, sfreq, freq, gain, fscale="linear", plot=("magnitude")
      )
      assert len(fig.axes) == 1
      plt.close("all")
      with pytest.raises(
          ValueError, match="Invalid value for the .plot"
      ):
          plot_filter(h, sfreq, freq, gain, plot=("turtles"))
      _, axes = plt.subplots(1)
      fig = plot_filter(
          h, sfreq, freq, gain, plot=("magnitude"), axes=axes
      )
      assert len(fig.axes) == 1
      _, axes = plt.subplots(2)
      fig = plot_filter(
          h, sfreq, freq, gain, plot=("magnitude", "delay"), axes=axes
      )
      assert len(fig.axes) == 2
      plt.close("all")
      _, axes = plt.subplots(1)
      with pytest.raises(ValueError, match="Length of axes"):
          plot_filter(
              h,
              sfreq,
              freq,
              gain,
              plot=("magnitude", "delay"),
              axes=axes,
          )
  
imports: from pathlib import Path
  import matplotlib.pyplot
  import numpy
  import pytest
  from numpy.testing import assert_array_equal
  from mne import SourceEstimate, pick_events, read_cov, read_dipole, read_events, read_evokeds, read_source_spaces
  from mne.chpi import compute_chpi_snr
  from mne.datasets import testing
  from mne.filter import create_filter
  from mne.io import read_raw_fif
  from mne.minimum_norm import read_inverse_operator
  from mne.time_frequency import CrossSpectralDensity
  from mne.viz import plot_bem, plot_chpi_snr, plot_csd, plot_events, plot_filter, plot_snr_estimate, plot_source_spectrogram
  from mne.viz.misc import _handle_event_colors
  from mne.viz.utils import _get_color_list
label_desc: Use image node_id 3 for calling a global function with example usage: test_plot_filter() without return types