code: def test_montage_grid_default_gray():
      n_images, n_rows, n_cols = 15, 11, 7
      arr_in = np.arange(n_images * n_rows * n_cols, dtype=float)
      arr_in = arr_in.reshape(n_images, n_rows, n_cols)
  
      n_tiles = int(np.ceil(np.sqrt(n_images)))
      arr_out = montage(arr_in)
      assert_equal(arr_out.shape, (n_tiles * n_rows, n_tiles * n_cols))
  
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 6 for calling a global function with example usage: test_montage_grid_default_gray() without return types