### Question:
StopWatch { public long taken() { if (start > 0 && stop > 0) { return stop - start; } else if (start > 0) { return System.currentTimeMillis() - start; } else { return 0; } } StopWatch();  StopWatch(boolean started); void restart(); long stop(); long taken();  }### Answer:
@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); }