Unit test to support the following issue report: https://github.com/bennidi/mbassador/issues/30

TestConcurrency.java

import static org.junit.Assert.assertTrue;
import java.util.concurrent.CountDownLatch;
import net.engio.mbassy.common.StrongConcurrentSet;
import org.junit.Test;

public class TestConcurrency {

    /**
     * In this test HashMap will cross capacity threshold multiple times in
     * different directions which will trigger rehashing. Because rehashing
     * requires modification of Entry class for all hash map entries some keys
     * may temporarily disappear from the map.
     * <p>
     * For more information please take a look at transfer method in HashMap.
     */
    @Test
    public void testConcurrentAddRemove() {
        final CountDownLatch latch = new CountDownLatch(1);
        final StrongConcurrentSet<Integer> set = new StrongConcurrentSet<Integer>();

        final int numItems = 8;

        // Adding elements that will not be t
        for (int i = 0; i < numItems; i++) {
            set.add(i);
        }

        // Adds and removes items >= numItems
        Thread updatingThread = new Thread() {
            public void run() {
                try {
                    latch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("Concurrent updates are running");
                for (int k = 0; k < 10000; k++) {
                    for (int i = numItems; i < 129; i++) {
                        set.add(i);
                    }
                    for (int i = numItems; i < 129; i++) {
                        set.remove(i);
                    }
                }
            };
        };
        updatingThread.start();

        // Making sure that all items are present in the set
        System.out.println("Concurrent updates are paused");
        for (int j = 0; j < numItems; j++) {
            assertTrue("Couldn't find " + j, set.contains(j));
        }

        System.out.println("Starting concurrent updates");
        latch.countDown();
        for (int i = 0; i < 100000; i++) {
            for (int j = 0; j < numItems; j++) {

                // Since elements from 0 to numItems are never removed,
                // set.contains(j) should always return true
                if (!set.contains(j)) {
                    System.out.println("Couldn't find " + j + " on attempt " + i);
                }
            }
        }
    }
}