Testing with Thread.sleep

Question

What are the recommended approaches to using Thread.sleep() to speed up tests.

I am testing a network library with a retry functionality when connection

Answer 1

I just faced a similar issue and I created a Sleeper interface to abstract this away:

public interface Sleeper
{
    void sleep( long millis ) throws InterruptedException;
}

The default implementation uses Thread.sleep():

public class ThreadSleeper implements Sleeper
{
    @Override
    public void sleep( long millis ) throws InterruptedException
    {
        Thread.sleep( millis );
    }
}

In my unit tests, I inject a FixedDateTimeAdvanceSleeper:

public class FixedDateTimeAdvanceSleeper implements Sleeper
{
    @Override
    public void sleep( long millis ) throws InterruptedException
    {
        DateTimeUtils.setCurrentMillisFixed( DateTime.now().getMillis() + millis );
    }
}

This allows me to query the time in a unit test:

assertThat( new DateTime( DateTimeUtils.currentTimeMillis() ) ).isEqualTo( new DateTime( "2014-03-27T00:00:30" ) );

Note that you need to fix the time first using DateTimeUtils.setCurrentMillisFixed( new DateTime( "2014-03-26T09:37:13" ).getMillis() ); at the start of your test and restore the time again after the test using DateTimeUtils.setCurrentMillisSystem();