public long taken() {
        if (start > 0 && stop > 0) {
            return stop - start;
        } else if (start > 0) {
            return System.currentTimeMillis() - start;
        } else {
            return 0;
        }
    }
@Test
    public void testStopWatchTaken() throws Exception {
        StopWatch watch = new StopWatch();
        Thread.sleep(100);
        long taken = watch.taken();
        Thread.sleep(100);
        long taken2 = watch.taken();
        assertNotSame(taken, taken2);
        assertTrue(taken2 > taken);
    }