svoid test_regionBorder_innerPoints() {
  BWImage img = bwImageFromString([[
    ____
    _xx_
    _xx_
    ____
  ]]);
  FastRegions_BWImage regions = new(img);
  regions.run();
  for (int i = 1; i <= regions.nRegions(); i++)
    print("Region " + i + ": " + map ptWithSlashes(regionBorder_innerPoints(regions, i)));
}