@Test
  public void testInvert() {
    RGB[][] rgbs = new RGB[2][2];
    rgbs[0][0] = Pixel.BLACK;
    rgbs[1][0] = Pixel.BLACK;
    rgbs[0][1] = Pixel.WHITE;
    rgbs[1][1] = Pixel.WHITE;

    Frame frame = new Frame(rgbs);
    print(frame);
    frame.invert();

    print(frame);
  }
 private void print(Frame frame) {
   System.out.println("printing");
   RGB[][] rgBs2 = frame.getRGBs();
   for (RGB[] rgbs3 : rgBs2) {
     for (RGB rgb : rgbs3) {
       System.out.println(rgb);
     }
   }
 }