code: def test_display_methods(img_3d_mni):
      """Tests display methods."""
      display = plot_img(img_3d_mni)
      display.add_overlay(img_3d_mni, threshold=0)
      display.add_edges(img_3d_mni, color="c")
      display.add_contours(
          img_3d_mni,
          contours=2,
          linewidth=4,
          colors=["limegreen", "yellow"],
      )
  
file_path: nilearn/nilearn/plotting/tests/test_img_plotting/test_plot_img.py
imports: import matplotlib.pyplot
  import numpy
  import pytest
  from nibabel import Nifti1Image
  from nilearn._utils.niimg import is_binary_niimg
  from nilearn.image import get_data
  from nilearn.plotting import plot_img
label_desc: Use image node_id 2 for calling a global function with example usage: test_display_methods(img_3d_mni) without return types