JUnit4 实际上不支持测试多线程程序。
The article at http://www.planetgeek.ch/2009/08/25/how-to-find-a-concurrency-bug-with-java/describes a method of exposing concurrency bugs that adds a new assertion method assertConcurrent.
该文章中提供了一个新的断言方法来测试多线程程序：
assertConcurrent(final String message, final List<? extends Runnable> runnables, final int maxTimeoutSeconds)
-
final String message：如果测试不通过，打印出的消息 -
final List<? extends Runnable> runnables：需要测试的线程 -
final int maxTimeoutSeconds：最长运行时间，单位 秒，如果超时，则测试不通过
该方法将需要测试的线程放入一个线程池中，并发执行，最后判断是否有异常发生，是否有超时发生。
示例如下：
如下的代码会产生超时，测试不通过。
java.lang.AssertionError: Test Failed timeout! More than1seconds
public class JUnit4_Test {
@Test
public void test1() throws Exception {
List<Runnable> runnables = new ArrayList<>(10);
for (int i = 0; i < 10; i++) {
runnables.add(new MyRunnable());
}
assertConcurrent("Test Failed", runnables, 1);
}
public static void assertConcurrent(final String message, final List<? extends Runnable> runnables, final int maxTimeoutSeconds) throws InterruptedException {
final int numThreads = runnables.size();
final List<Throwable> exceptions = Collections.synchronizedList(new ArrayList<Throwable>());
final ExecutorService threadPool = Executors.newFixedThreadPool(numThreads);
try {
final CountDownLatch allExecutorThreadsReady = new CountDownLatch(numThreads);
final CountDownLatch afterInitBlocker = new CountDownLatch(1);
final CountDownLatch allDone = new CountDownLatch(numThreads);
for (final Runnable submittedTestRunnable : runnables) {
threadPool.submit(new Runnable() {
public void run() {
allExecutorThreadsReady.countDown();
try {
afterInitBlocker.await();
submittedTestRunnable.run();
} catch (final Throwable e) {
exceptions.add(e);
} finally {
allDone.countDown();
}
}
});
}
// wait until all threads are ready
assertTrue("Timeout initializing threads! Perform long lasting initializations before passing runnables to assertConcurrent", allExecutorThreadsReady.await(runnables.size() * 10, TimeUnit.MILLISECONDS));
// start all test runners
afterInitBlocker.countDown();
assertTrue(message + " timeout! More than" + maxTimeoutSeconds + "seconds", allDone.await(maxTimeoutSeconds, TimeUnit.SECONDS));
} finally {
threadPool.shutdownNow();
}
assertTrue(message + "failed with exception(s)" + exceptions, exceptions.isEmpty());
}
}
class MyRunnable implements Runnable {
public void run() {
try {
Thread.sleep(10000);
} catch (Exception e) {
} finally {
}
}
}
