@Test
    public void testNextImage1() {
        ValidationCode vc = new ValidationCode();
        RenderedImage image = vc.nextImage(4, true);
        try {
            ImageIO.write(image, "PNG", new File("d:\\test\\test.png")); 
        } catch(Exception e) {
            
        }
        String str= vc.getValidationCode();
        assertThat(str.length(),  is(4));
    }