Add support to decode Device, Port, Link JSON.

- Device, Port, Link can now be encoded and decoded back to Java Object,
  which will be Object#equals to the original.
- Modified DeviceServiceAdapter to be null-safe when possible
- Modified JSON assertion/matcher not to check for exact number of attributes

Change-Id: I7cf02e2254cf17f6265fb15847912519e564b14f
diff --git a/core/common/src/test/java/org/onosproject/codec/impl/LinkCodecTest.java b/core/common/src/test/java/org/onosproject/codec/impl/LinkCodecTest.java
new file mode 100644
index 0000000..c44b0eb
--- /dev/null
+++ b/core/common/src/test/java/org/onosproject/codec/impl/LinkCodecTest.java
@@ -0,0 +1,54 @@
+/*
+ * 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.codec.impl;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.onosproject.codec.impl.JsonCodecUtils.assertJsonEncodable;
+
+import org.junit.Test;
+import org.onosproject.codec.JsonCodec;
+import org.onosproject.net.DefaultLink;
+import org.onosproject.net.Link;
+import org.onosproject.net.device.DeviceService;
+import org.onosproject.net.device.DeviceServiceAdapter;
+
+/**
+ * Unit test for LinkCodec.
+ */
+public class LinkCodecTest {
+
+    private final Link link = new DefaultLink(JsonCodecUtils.PID,
+                                              JsonCodecUtils.CP1,
+                                              JsonCodecUtils.CP2,
+                                              Link.Type.DIRECT,
+                                              Link.State.ACTIVE,
+                                              false,
+                                              JsonCodecUtils.A1);
+
+    @Test
+    public void linkCodecTest() {
+        final MockCodecContext context = new MockCodecContext();
+        context.registerService(DeviceService.class, new DeviceServiceAdapter());
+        final JsonCodec<Link> codec = context.codec(Link.class);
+        assertThat(codec, is(notNullValue()));
+        final Link pojoIn = link;
+
+        assertJsonEncodable(context, codec, pojoIn);
+    }
+}