code: def test_edge_detect():
      img = np.zeros((10, 10))
      img[:5] = 1
      _, _ = _edge_detect(img)
      np.testing.assert_almost_equal(img[4], 1)
  
imports: import numpy
  from nilearn.plotting.edge_detect import _edge_detect
label_desc: Use image node_id 1 for calling a global function with example usage: test_edge_detect() without return types