code: def test_montage_simple_gray():
      n_images, n_rows, n_cols = 3, 2, 3
      arr_in = np.arange(n_images * n_rows * n_cols, dtype=float)
      arr_in = arr_in.reshape(n_images, n_rows, n_cols)
  
      arr_out = montage(arr_in)
      arr_ref = np.array(
          [
              [0.0, 1.0, 2.0, 6.0, 7.0, 8.0],
              [3.0, 4.0, 5.0, 9.0, 10.0, 11.0],
              [12.0, 13.0, 14.0, 8.5, 8.5, 8.5],
              [15.0, 16.0, 17.0, 8.5, 8.5, 8.5],
          ]
      )
      assert_array_equal(arr_out, arr_ref)
  
file_path: scikit-image/skimage/util/tests/test_montage.py
imports: from skimage._shared import testing
  from skimage._shared.testing import assert_equal, assert_array_equal
  import numpy
  from skimage.util import montage
label_desc: Use image node_id 1 for calling a global function with example usage: test_montage_simple_gray() without return types