Index: trunk/test/unit/org/openstreetmap/josm/tools/ListenableWeakReferenceTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/tools/ListenableWeakReferenceTest.java	(revision 12181)
+++ trunk/test/unit/org/openstreetmap/josm/tools/ListenableWeakReferenceTest.java	(revision 12181)
@@ -0,0 +1,55 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.tools;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.openstreetmap.josm.testutils.JOSMTestRules;
+
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+
+/**
+ * Tests for {@link ListenableWeakReference}
+ * @author Michael Zangl
+ * @since 12181
+ */
+public class ListenableWeakReferenceTest {
+    /**
+     * Default test rules.
+     */
+    @Rule
+    @SuppressFBWarnings(value = "URF_UNREAD_PUBLIC_OR_PROTECTED_FIELD")
+    public JOSMTestRules test = new JOSMTestRules();
+    private Object object;
+    private boolean called;
+
+    /**
+     * Tests that {@link ListenableWeakReference#onDereference()} is called.
+     * @throws InterruptedException never
+     */
+    @Test
+    public void testOnDereference() throws InterruptedException {
+        object = new Object();
+        called = false;
+        ListenableWeakReference<Object> weak = new ListenableWeakReference<>(object, () -> called = true);
+        assertFalse(called);
+        assertSame(object, weak.get());
+
+        // now delete it
+        object = null;
+        System.gc();
+        System.runFinalization();
+        // now we wait for the listener thread
+        Thread.sleep(200);
+        assertTrue(called);
+
+        assertNotNull(weak);
+        assertNull(weak.get());
+    }
+
+}