def METHOD_NAME(shape, spacing):
    grid = RasterModelGrid(shape, xy_spacing=spacing)
    value_at_link = np.random.uniform(size=grid.number_of_links)
    actual = grid.empty(at="node")
    expected = calc_diff_at_link_slow(grid, value_at_link)
    actual = calc_diff_at_link(grid, value_at_link)
    assert_array_almost_equal(actual, expected)