svoid test_BWImage() {
  assertEqualsVerbose(0.5, BWImage(2, 2, 0.5f).averageBrightness());
  assertEqualsVerbose(0.25, BWImage(2, 2, 0.25f).averageBrightness());
  assertEqualsVerbose(0.75, BWImage(2, 2, new float[] {0, 1, 1, 1}).averageBrightness());
}