Renamed AbstractListenerRegistry to ListenerRegistry (since it is not abstract).
- added checkForNonRegistrant() predicate and augmented unit tests.

Change-Id: I7ecc618f01fdc4cead6f143a1e5e0ddd03268efc
diff --git a/core/api/src/main/java/org/onosproject/event/AbstractListenerRegistry.java b/core/api/src/main/java/org/onosproject/event/ListenerRegistry.java
similarity index 79%
rename from core/api/src/main/java/org/onosproject/event/AbstractListenerRegistry.java
rename to core/api/src/main/java/org/onosproject/event/ListenerRegistry.java
index 38575a4..4164441 100644
--- a/core/api/src/main/java/org/onosproject/event/AbstractListenerRegistry.java
+++ b/core/api/src/main/java/org/onosproject/event/ListenerRegistry.java
@@ -28,15 +28,20 @@
  * Base implementation of an event sink and a registry capable of tracking
  * listeners and dispatching events to them as part of event sink processing.
  */
-public class AbstractListenerRegistry<E extends Event, L extends EventListener<E>>
+public class ListenerRegistry<E extends Event, L extends EventListener<E>>
         implements EventSink<E> {
 
     private final Logger log = getLogger(getClass());
 
-    protected final Set<L> listeners = new CopyOnWriteArraySet<>();
     private volatile boolean shutdown = false;
 
     /**
+     * Set of listeners that have registered.
+     */
+    protected final Set<L> listeners = new CopyOnWriteArraySet<>();
+
+
+    /**
      * Adds the specified listener.
      *
      * @param listener listener to be added
@@ -53,7 +58,9 @@
      */
     public void removeListener(L listener) {
         checkNotNull(listener, "Listener cannot be null");
-        checkArgument(listeners.remove(listener), "Listener not registered");
+        if (checkForNonRegistrant()) {
+            checkArgument(listeners.remove(listener), "Listener not registered");
+        }
     }
 
     @Override
@@ -68,6 +75,19 @@
     }
 
     /**
+     * Predicate indicating whether we should throw an exception if the
+     * argument to {@link #removeListener} is not in the current set of
+     * listeners.
+     * <p>
+     * This default implementation returns <code>true</code>.
+     *
+     * @return true if non-listed listeners should cause exception on remove
+     */
+    protected boolean checkForNonRegistrant() {
+        return true;
+    }
+
+    /**
      * Reports a problem encountered while processing an event.
      *
      * @param event event being processed
@@ -92,5 +112,4 @@
     public void deactivate() {
         shutdown = true;
     }
-
 }
diff --git a/core/api/src/test/java/org/onosproject/event/AbstractListenerRegistryTest.java b/core/api/src/test/java/org/onosproject/event/AbstractListenerRegistryTest.java
deleted file mode 100644
index 96613f2..0000000
--- a/core/api/src/test/java/org/onosproject/event/AbstractListenerRegistryTest.java
+++ /dev/null
@@ -1,64 +0,0 @@
-/*
- * Copyright 2014 Open Networking Laboratory
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.onosproject.event;
-
-import org.junit.Test;
-
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertTrue;
-
-/**
- * Tests of the base listener manager.
- */
-public class AbstractListenerRegistryTest {
-
-    @Test
-    public void basics() {
-        TestListener listener = new TestListener();
-        TestListener secondListener = new TestListener();
-        TestListenerRegistry manager = new TestListenerRegistry();
-        manager.addListener(listener);
-        manager.addListener(secondListener);
-
-        TestEvent event = new TestEvent(TestEvent.Type.BAR, "bar");
-        manager.process(event);
-        assertTrue("event not processed", listener.events.contains(event));
-        assertTrue("event not processed", secondListener.events.contains(event));
-
-        manager.removeListener(listener);
-
-        TestEvent another = new TestEvent(TestEvent.Type.FOO, "foo");
-        manager.process(another);
-        assertFalse("event processed", listener.events.contains(another));
-        assertTrue("event not processed", secondListener.events.contains(event));
-    }
-
-    @Test
-    public void badListener() {
-        TestListener listener = new BrokenListener();
-        TestListener secondListener = new TestListener();
-        TestListenerRegistry manager = new TestListenerRegistry();
-        manager.addListener(listener);
-        manager.addListener(secondListener);
-
-        TestEvent event = new TestEvent(TestEvent.Type.BAR, "bar");
-        manager.process(event);
-        assertFalse("event processed", listener.events.contains(event));
-        assertFalse("error not reported", manager.errors.isEmpty());
-        assertTrue("event not processed", secondListener.events.contains(event));
-    }
-
-}
diff --git a/core/api/src/test/java/org/onosproject/event/ListenerRegistryTest.java b/core/api/src/test/java/org/onosproject/event/ListenerRegistryTest.java
new file mode 100644
index 0000000..5645926
--- /dev/null
+++ b/core/api/src/test/java/org/onosproject/event/ListenerRegistryTest.java
@@ -0,0 +1,93 @@
+/*
+ * Copyright 2014 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.event;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Unit tests for {@link ListenerRegistry}.
+ */
+public class ListenerRegistryTest {
+
+    private static class RelaxedRegistry extends TestListenerRegistry {
+        @Override
+        protected boolean checkForNonRegistrant() {
+            return false;
+        }
+    }
+
+    private static final TestEvent FOO_EVENT =
+            new TestEvent(TestEvent.Type.FOO, "foo");
+    private static final TestEvent BAR_EVENT =
+            new TestEvent(TestEvent.Type.BAR, "bar");
+
+    private TestListener listener;
+    private TestListener secondListener;
+    private TestListenerRegistry manager;
+
+    @Before
+    public void setUp() {
+        listener = new TestListener();
+        secondListener = new TestListener();
+        manager = new TestListenerRegistry();
+    }
+
+    @Test
+    public void basics() {
+        manager.addListener(listener);
+        manager.addListener(secondListener);
+
+        manager.process(BAR_EVENT);
+        assertTrue("BAR not processed", listener.events.contains(BAR_EVENT));
+        assertTrue("BAR not processed", secondListener.events.contains(BAR_EVENT));
+
+        manager.removeListener(listener);
+
+        manager.process(FOO_EVENT);
+        assertFalse("FOO processed", listener.events.contains(FOO_EVENT));
+        assertTrue("FOO not processed", secondListener.events.contains(FOO_EVENT));
+    }
+
+    @Test
+    public void badListener() {
+        listener = new BrokenListener();
+
+        manager.addListener(listener);
+        manager.addListener(secondListener);
+
+        manager.process(BAR_EVENT);
+        assertFalse("BAR processed", listener.events.contains(BAR_EVENT));
+        assertFalse("error not reported", manager.errors.isEmpty());
+        assertTrue("BAR not processed", secondListener.events.contains(BAR_EVENT));
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void removeNonListenerCausesException() {
+        manager.removeListener(listener);
+    }
+
+    @Test
+    public void removeNonListenerIgnored() {
+        manager = new RelaxedRegistry();
+        manager.removeListener(listener);
+        assertTrue("what?", manager.listeners.isEmpty());
+    }
+
+}
diff --git a/core/api/src/test/java/org/onosproject/event/TestListenerRegistry.java b/core/api/src/test/java/org/onosproject/event/TestListenerRegistry.java
index 0b9770e..fd9b6d0 100644
--- a/core/api/src/test/java/org/onosproject/event/TestListenerRegistry.java
+++ b/core/api/src/test/java/org/onosproject/event/TestListenerRegistry.java
@@ -22,7 +22,7 @@
  * Test event listener manager fixture.
  */
 public class TestListenerRegistry
-        extends AbstractListenerRegistry<TestEvent, TestListener> {
+        extends ListenerRegistry<TestEvent, TestListener> {
 
     public final List<Throwable> errors = new ArrayList<>();