How can I make a JUnit test wait

Question

I have a JUnit test that I want to wait for a period of time synchronously  My JUnit test looks like this   Test public void testExipres        SomeCacheObject sco   new SomeCacheObject        sco putWithExipration  quot foo quot   1000          WAIT FOR 2 SECONDS     assertNull sco getIfNotExipred  quot foo quot        I tried Thread currentThread   wait    but it throws an IllegalMonitorStateException  as expected   Is there some trick to it or do I need a different monitor

User · Answer

You can use java util concurrent TimeUnit library which internally uses Thread sleep  The syntax should look like this      Test public void testExipres        SomeCacheObject sco   new SomeCacheObject        sco putWithExipration  foo   1000        TimeUnit MINUTES sleep 2        assertNull sco getIfNotExipred  foo         This library provides more clear interpretation for time unit  You can use  HOURS   MINUTES   SECONDS

User · Answer

If it is an absolute must to generate delay in a test CountDownLatch is a simple solution  In your test class declare  private final CountDownLatch waiter   new CountDownLatch 1    and in the test where needed  waiter await 1000   1000  TimeUnit NANOSECONDS      1ms  Maybe unnecessary to say but keeping in mind that you should keep wait times small and not cumulate waits to too many places

User · Answer

Thread sleep   could work in most cases  but usually if you re waiting  you are actually waiting for a particular condition or state to occur   Thread sleep   does not guarantee that whatever you re waiting for has actually happened     If you are waiting on a rest request for example maybe it usually return in 5 seconds  but if you set your sleep for 5 seconds the day your request comes back in 10 seconds your test is going to fail   To remedy this JayWay has a great utility called Awatility which is perfect for ensuring that a specific condition occurs before you move on   It has a nice fluent api as well  await   until    - gt         return yourConditionIsMet            https   github com jayway awaitility

User · Answer

You could also use the CountDownLatch object like explained here

User · Answer

In case your static code analyzer  like SonarQube  complaints  but you can not think of another way  rather than sleep  you may try with a hack like  Awaitility await   pollDelay Durations ONE SECOND  until    - gt  true   It s conceptually incorrect  but it is the same as Thread sleep 1000    The best way  of course  is to pass a Callable  with your appropriate condition  rather than true  which I have   https   github com awaitility awaitility

User · Answer

How about Thread sleep 2000

User · Answer

There is a general problem  it s hard to mock time  Also  it s really bad practice to place long running waiting code in a unit test  So  for making a scheduling API testable  I used an interface with a real and a mock implementation like this  public interface Clock            public long getCurrentMillis             public void sleep long millis  throws InterruptedException          public static class SystemClock implements Clock         Override     public long getCurrentMillis             return System currentTimeMillis                Override     public void sleep long millis  throws InterruptedException           Thread sleep millis                 public static class MockClock implements Clock        private final AtomicLong currentTime   new AtomicLong 0             public MockClock             this System currentTimeMillis                    public MockClock long currentTime            this currentTime set currentTime                    Override     public long getCurrentMillis             return currentTime addAndGet 5               Override     public void sleep long millis            currentTime addAndGet millis                 With this  you could imitate time in your test   Test public void testExpiration         MockClock clock   new MockClock        SomeCacheObject sco   new SomeCacheObject        sco putWithExpiration  quot foo quot   1000       clock sleep 2000     wait for 2 seconds     assertNull sco getIfNotExpired  quot foo quot        An advanced multi-threading mock for Clock is much more complex  of course  but you can make it with ThreadLocal references and a good time synchronization strategy  for example

[java] How can I make a JUnit test wait?

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