svoid test_QuadTreeBitMatrix() {
  // 4*4, one pixel white
  BitSetMatrix m = new(4, 4);
  m.set(1, 1);
  QuadTreeBitMatrix qt = bitMatrixToQuadTree(m);
  assertTrueVerbose(equal := eqMatrices(m, qt));
  assertEqualsVerbose(2, qt.compositeNodeCount());
  
  // turn pixel back to black
  qt.set(1, 1, false);
  m.set(1, 1, false);
  assertTrueVerbose(equal := eqMatrices(m, qt));
  print(structure(qt));
  qt.set(1, 1, false);
  print(structure(qt));
  assertEqualsVerbose(0, qt.compositeNodeCount());
  
  // all pixels white
  for y to 4:
    for x to 4:
      qt.set(x, y);
  assertEqualsVerbose(0, qt.compositeNodeCount());
  
  test_QuadTreeBitMatrix_2();
}

svoid test_QuadTreeBitMatrix_2() {
  for (double p = .1; p < 1; p += .1) {
    new Average nodes;
    repeat 100 {
      var matrix = randomBitMatrix(8, 8, p);
      QuadTreeBitMatrix qt = bitMatrixToQuadTree(matrix);
      nodes.add(qt.compositeNodeCount());
      assertTrue(eqMatrices(matrix, qt));
    }
    printVars(+p, +nodes);
  }
}