svoid test_RegionBorder_innerPoints_thinSpike() {
  //set flag RegionBorder_innerPoints_debug.
  //set flag FastRegions_debug.
  BWImage img = bwImageFromString([[
    ______
    _xxxx_
    _xx___
    ______
  ]]);
  FastRegions_BWImage regions = new(img);
  regions.run();
  assertEqualsVerbose(2, regions.nRegions());
  RegionBorder_innerPoints border = new(regions, 2);
  var points = border.allPoints();
  //removeLastIfSameAsFirst(points);
  assertEqualsVerbose(litpts(1, 1, 2, 1, 3, 1, 4, 1, 3, 1, 2, 1, 2, 2, 1, 2), points);
  assertEqualsVerbose("44488682", str(border.onePath()));
}