svoid test_g22_regionFilledness() {
  BWImage img = bwImageFromString([[
    ___xx_
    ___x__
    __x__x
    __xx_x
    ______
    _xx___
  ]]);
  FastRegions_BWImage regions = new(img);
  regions.run();
  printStruct(regions.regionsBySize);
  for (i : regions.regionsRoughlyByDecreasingSize())
    printVars(+i,
      pixels := regions.regionSize(i),
      filledness := g22_regionFilledness(regions.get(i)),
      color := regions.get(i).color());
}

Began life as a copy of #1033951