Why can't wake up this thread

Question

I want to test Thread.sleep() method, and I found a interesting thing.. When I invoke main() method , the console will print "UserA sleeping..." and "UserA waking...", that means the program is awakened , but when I use a junit method to run the same code as main() method, it won't print "UserA waking..." ... I will be appreciate anyone can explain it .

package com.lmh.threadlocal;

import org.junit.Test;

public class ThreadTest {

    public static void main(String [] args) {
        new Thread(new UserA()).start();
    }
    @Test
    public void testWakeup(){
        new Thread(new UserA()).start();
    }

}

class UserA implements Runnable{
    @Override
    public void run() {
        try {
            System.out.println("UserA sleeping...");
            Thread.sleep(1000);
            System.out.println("UserA waking...");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}

Answer 1

My guess is that JUnit is tearing down the test before the sleep finishes, because the test execution thread exits the test method before the sleep finishes. Try

@Test
public void testWakeup() throws Exception {
    Thread t = new Thread(new UserA());
    t.start();
    t.join();
}