code: @Test public void testRectangularMatrix(){
    BitMatrix matrix=new BitMatrix(75,20);
    assertEquals(75,matrix.getWidth());
    assertEquals(20,matrix.getHeight());
    matrix.set(10,0);
    matrix.set(11,1);
    matrix.set(50,2);
    matrix.set(51,3);
    matrix.flip(74,4);
    matrix.flip(0,5);
    assertTrue(matrix.get(10,0));
    assertTrue(matrix.get(11,1));
    assertTrue(matrix.get(50,2));
    assertTrue(matrix.get(51,3));
    assertTrue(matrix.get(74,4));
    assertTrue(matrix.get(0,5));
    matrix.flip(50,2);
    matrix.flip(51,3);
    assertFalse(matrix.get(50,2));
    assertFalse(matrix.get(51,3));
  }
  