diff --git a/core/api/src/test/java/org/onosproject/ui/topo/ModTest.java b/core/api/src/test/java/org/onosproject/ui/topo/ModTest.java
new file mode 100644
index 0000000..bb40279
--- /dev/null
+++ b/core/api/src/test/java/org/onosproject/ui/topo/ModTest.java
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2015 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.ui.topo;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+/**
+ * Unit tests for {@link Mod}.
+ */
+public class ModTest {
+
+    private static final String AAA = "aaa";
+    private static final String BBB = "bbb";
+
+    private Mod mod1;
+    private Mod mod2;
+
+    @Test(expected = NullPointerException.class)
+    public void nullId() {
+        new Mod(null);
+    }
+
+    @Test
+    public void basic() {
+        mod1 = new Mod(AAA);
+        assertEquals("wrong id", AAA, mod1.toString());
+    }
+
+    @Test
+    public void equivalence() {
+        mod1 = new Mod(AAA);
+        mod2 = new Mod(AAA);
+        assertNotSame("oops", mod1, mod2);
+        assertEquals("not equivalent", mod1, mod2);
+    }
+
+    @Test
+    public void comparable() {
+        mod1 = new Mod(AAA);
+        mod2 = new Mod(BBB);
+        assertNotEquals("what?", mod1, mod2);
+        assertTrue(mod1.compareTo(mod2) < 0);
+        assertTrue(mod2.compareTo(mod1) > 0);
+    }
+}