svoid test_HashedBWImage() {
  var img1 = randomImage(10);
  var himg1 = new HashedBWImage(img1);
  var himg2 = new HashedBWImage(img1);
  assertEquals(himg1.hashCode(), himg2.hashCode());
  assertEquals(himg1.hash(), himg2.hash());
  assertEquals(himg1, himg2);
  
  var img3 = randomImage(10);
  var himg3 = new HashedBWImage(img3);
  assertNotEquals(himg1.hashCode(), himg3.hashCode());
  assertNotEquals(himg1.hash(), himg3.hash());
  assertNotEquals(himg1, himg3);
}