svoid test_ImageSimilarityAtScale_equalImages() {
  var img = randomImage(50, 20);
  var ii = IntegralImage(img);
  ImageSimilarityAtScale algo = new(ii, ii, 4);
  algo.run();
  repeat 256 {
    assertTrue(algo.step());
    assertEquals(0.0, algo.diff());
  }
  assertFalse(algo.step());
}