code: def test_plot_heatmap(axes):
      """Test plot_gaze."""
      # Create a toy epochs instance
      info = info = mne.create_info(
          ch_names=["xpos", "ypos"], sfreq=100, ch_types="eyegaze"
      )
      # simulate a steady fixation at the center of the screen
      width, height = (1920, 1080)
      shape = (1, 100)  # x or y, time
      data = np.vstack(
          [np.full(shape, width / 2), np.full(shape, height / 2)]
      )
      epochs = mne.EpochsArray(data[None, ...], info)
      epochs.info["chs"][0]["loc"][4] = -1
      epochs.info["chs"][1]["loc"][4] = 1
  
      if axes:
          axes = plt.subplot()
      fig = mne.viz.eyetracking.plot_gaze(
          epochs,
          width=width,
          height=height,
          axes=axes,
          cmap="Greys",
          sigma=None,
      )
      img = fig.axes[0].images[0].get_array()
      # We simulated a 2D histogram where only the central pixel (960, 540) was active
      assert (
          img.T[width // 2, height // 2] == 1
      )  # central pixel is active
      assert np.sum(img) == 1
  
imports: import matplotlib.pyplot
  import numpy
  import pytest
  import mne
label_desc: Use image node_id 1 for calling a global function with example usage: test_plot_heatmap(axes) without return types