Added a unit test for the simple event dispatcher.

+package org.onlab.onos.event.impl;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.onlab.onos.event.AbstractEvent;
+import org.onlab.onos.event.EventSink;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Test of the even dispatcher mechanism.
+ */
+public class SimpleEventDispatcherTest {
+
+    private final SimpleEventDispatcher dispatcher = new SimpleEventDispatcher();
+    private final PrickleSink prickleSink = new PrickleSink();
+    private final GooSink gooSink = new GooSink();
+
+    @Before
+    public void setUp() {
+        dispatcher.activate();
+        dispatcher.addSink(Prickle.class, prickleSink);
+        dispatcher.addSink(Goo.class, gooSink);
+    }
+
+    @After
+    public void tearDown() {
+        dispatcher.removeSink(Goo.class);
+        dispatcher.removeSink(Prickle.class);
+        dispatcher.deactivate();
+    }
+
+    @Test
+    public void post() throws Exception {
+        prickleSink.latch = new CountDownLatch(1);
+        dispatcher.post(new Prickle("yo"));
+        prickleSink.latch.await(100, TimeUnit.MILLISECONDS);
+        validate(prickleSink, "yo");
+        validate(gooSink);
+    }
+
+    @Test
+    public void postEventWithBadSink() throws Exception {
+        gooSink.latch = new CountDownLatch(1);
+        dispatcher.post(new Goo("boom"));
+        gooSink.latch.await(100, TimeUnit.MILLISECONDS);
+        validate(gooSink, "boom");
+        validate(prickleSink);
+    }
+
+    @Test
+    public void postEventWithNoSink() throws Exception {
+        dispatcher.post(new Thing("boom"));
+        validate(gooSink);
+        validate(prickleSink);
+    }
+
+    private void validate(Sink sink, String... strings) {
+        int i = 0;
+        assertEquals("incorrect event count", strings.length, sink.subjects.size());
+        for (String string : strings) {
+            assertEquals("incorrect event", string, sink.subjects.get(i++));
+        }
+    }
+
+    private enum Type { FOO };
+
+    private static class Thing extends AbstractEvent<Type, String> {
+        protected Thing(String subject) {
+            super(Type.FOO, subject);
+        }
+    }
+
+    private static class Prickle extends Thing {
+        protected Prickle(String subject) {
+            super(subject);
+        }
+    }
+
+    private static class Goo extends Thing {
+        protected Goo(String subject) {
+            super(subject);
+        }
+    }
+
+    private static class Sink {
+        final List<String> subjects = new ArrayList<>();
+        CountDownLatch latch;
+
+        protected void process(String subject) {
+            subjects.add(subject);
+            latch.countDown();
+        }
+    }
+
+    private static class PrickleSink extends Sink implements EventSink<Prickle> {
+        @Override
+        public void process(Prickle event) {
+            process(event.subject());
+        }
+    }
+
+    private static class GooSink extends Sink implements EventSink<Goo> {
+        @Override
+        public void process(Goo event) {
+            process(event.subject());
+            throw new IllegalStateException("BOOM!");
+        }
+    }
+
+}