When executor meets Thread.sleep, why the thread ends without sleeping or throw InterruptedException?

I do not know why junit has the following behavior:

When I submit a thread into a executor (fixedThreadPool or others) while the thread has a sleep behavior (Thread.sleep()), I find that the thread ends up immediately! No sleeping, no interruptedExcetion.

I wonder why?

(I know the following design is not good, but I just want to describe the above question)

@Test
public void executorPoolTest(){
    ExecutorService cachedThreadPool = 
            Executors.newFixedThreadPool(10);
    //Executors.newCachedThreadPool();  
    for (int i = 0; i < 1000; i++) {  
        final int index = i;  
        cachedThreadPool.execute(new Runnable() {  
            public void run() {  
                System.out.println(index);
                try {  
                    Thread.sleep( 5000); 
                    System.out.println(index+"_");
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
            }  
        });  
    }
    //no matter whether you call shutdown, the above program will ends quickly.
    cachedThreadPool.shutdown();

}

The above program do not print any number+"_", very strange. However, if the above method is running in a main method (I mean: public static void main(String[] args)), the behavior is normal, the threads will sleep and "_" can be printed.

I wonder why? What happened in junit framework? If so, can't I use junit to test executor involved methods?

The junit version is 4.12.

<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
</dependency>