// finder: RGBImage -> L<Rect>
static void testIconFinder(O finder, RGBImage inputImage1, RGBImage inputImage2, Pt positionInImage1, Pt positionInImage2) {
  L<Rect> l1 = (L) callF(finder, inputImage1);
  L<Rect> l2 = (L) callF(finder, inputImage2);
  assertTrue(containsPoint(l1, positionInImage1) && !containsPoint(l2, positionInImage2));
  assertTrue(containsPoint(l2, positionInImage2) && !containsPoint(l2, positionInImage1));
  print("ok");
}