Implement basic unit tests for RouteHandler

In addition,
    - Refactor Segment Routing unit test mocking

Change-Id: I94cb75a8b12944264faa76301d58ee19f246d584
diff --git a/src/test/java/org/onosproject/segmentrouting/MockDefaultRoutingHandler.java b/src/test/java/org/onosproject/segmentrouting/MockDefaultRoutingHandler.java
new file mode 100644
index 0000000..a69d5e7
--- /dev/null
+++ b/src/test/java/org/onosproject/segmentrouting/MockDefaultRoutingHandler.java
@@ -0,0 +1,52 @@
+/*
+ * Copyright 2017-present Open Networking Foundation
+ *
+ * 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.segmentrouting;
+
+import org.onlab.packet.IpPrefix;
+import org.onosproject.net.ConnectPoint;
+
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Mock Default Routing Handler.
+ */
+public class MockDefaultRoutingHandler extends DefaultRoutingHandler {
+    private Map<ConnectPoint, Set<IpPrefix>> subnetTable;
+
+    MockDefaultRoutingHandler(SegmentRoutingManager srManager,
+                              Map<ConnectPoint, Set<IpPrefix>> subnetTable) {
+        super(srManager);
+        this.subnetTable = subnetTable;
+    }
+
+    @Override
+    protected void populateSubnet(Set<ConnectPoint> cpts, Set<IpPrefix> subnets) {
+        cpts.forEach(cpt -> subnetTable.put(cpt, subnets));
+    }
+
+    @Override
+    protected boolean revokeSubnet(Set<IpPrefix> subnets) {
+        for (Map.Entry<ConnectPoint, Set<IpPrefix>> entry : subnetTable.entrySet()) {
+            entry.getValue().removeAll(subnets);
+            if (entry.getValue().isEmpty()) {
+                subnetTable.remove(entry.getKey());
+            }
+        }
+        return true;
+    }
+}
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