diff --git a/src/test/java/net/onrc/onos/core/intent/MockNetworkGraph.java b/src/test/java/net/onrc/onos/core/intent/MockNetworkGraph.java
new file mode 100644
index 0000000..fce9cc2
--- /dev/null
+++ b/src/test/java/net/onrc/onos/core/intent/MockNetworkGraph.java
@@ -0,0 +1,99 @@
+package net.onrc.onos.core.intent;
+
+import net.onrc.onos.ofcontroller.networkgraph.NetworkGraph;
+import net.onrc.onos.ofcontroller.networkgraph.NetworkGraphImpl;
+import net.onrc.onos.ofcontroller.networkgraph.Link;
+import net.onrc.onos.ofcontroller.networkgraph.LinkImpl;
+import net.onrc.onos.ofcontroller.networkgraph.Port;
+import net.onrc.onos.ofcontroller.networkgraph.Switch;
+import net.onrc.onos.ofcontroller.networkgraph.SwitchImpl;
+
+/**
+ * A mock class of NetworkGraph.
+ * This class should be used only by test codes.
+ *
+ * @author Toshio Koide (t-koide@onlab.us)
+ */
+public class MockNetworkGraph extends NetworkGraphImpl {
+	public static Long LOCAL_PORT = 0xFFFEL;
+	public SwitchImpl sw1, sw2, sw3, sw4;
+
+	class DetachableLinkImpl extends LinkImpl {
+		public DetachableLinkImpl(NetworkGraph graph, Port srcPort, Port dstPort) {
+			super(graph, srcPort, dstPort);
+		}
+
+		public void detachFromGraph() {
+			unsetFromPorts();
+		}
+	}
+	public Switch addSwitch(Long switchId) {
+		SwitchImpl sw = new SwitchImpl(this, switchId);
+		this.putSwitch(sw);
+		return sw;
+	}
+
+	public Link addLink(Long srcDpid, Long srcPortNo, Long dstDpid, Long dstPortNo) {
+		return new DetachableLinkImpl(
+				this,
+				getSwitch(srcDpid).getPort(srcPortNo),
+				getSwitch(dstDpid).getPort(dstPortNo));
+	}
+
+	public Link[] addBidirectionalLinks(Long srcDpid, Long srcPortNo, Long dstDpid, Long dstPortNo) {
+		Link[] links = new Link[2];
+		links[0] = addLink(srcDpid, srcPortNo, dstDpid, dstPortNo);
+		links[1] = addLink(dstDpid, dstPortNo, srcDpid, srcPortNo);
+
+		return links;
+	}
+
+	/**
+	 * create sample topology of 4 switches and 5 bidirectional links.
+	 * <pre>
+	 * [1] --- [2]
+	 *  |    /  |
+	 *  |  /    |
+	 * [4] --- [3]
+	 * </pre>
+	 */
+	public void createSampleTopology1() {
+		sw1 = (SwitchImpl) addSwitch(1L);
+		sw1.addPort(LOCAL_PORT);
+		sw2 = (SwitchImpl) addSwitch(2L);
+		sw2.addPort(LOCAL_PORT);
+		sw3 = (SwitchImpl) addSwitch(3L);
+		sw3.addPort(LOCAL_PORT);
+		sw4 = (SwitchImpl) addSwitch(4L);
+		sw4.addPort(LOCAL_PORT);
+
+		sw1.addPort(12L); // sw1 -> sw2
+		sw1.addPort(14L); // sw1 -> sw4
+		sw2.addPort(21L); // sw2 -> sw1
+		sw2.addPort(23L); // sw2 -> sw3
+		sw2.addPort(24L); // sw2 -> sw4
+		sw3.addPort(32L); // sw3 -> sw2
+		sw3.addPort(34L); // sw3 -> sw4
+		sw4.addPort(41L); // sw4 -> sw1
+		sw4.addPort(42L); // sw4 -> sw2
+		sw4.addPort(43L); // sw4 -> sw3
+
+		addBidirectionalLinks(1L, 12L, 2L, 21L);
+		addBidirectionalLinks(2L, 23L, 3L, 32L);
+		addBidirectionalLinks(3L, 34L, 4L, 43L);
+		addBidirectionalLinks(4L, 41L, 1L, 14L);
+		addBidirectionalLinks(2L, 24L, 4L, 42L);
+
+		// set capacity of all links to 1000Mbps
+		for (Link link: getLinks()) {
+			((LinkImpl)link).setCapacity(1000.0);
+		}
+	}
+
+	public void removeLink(Long srcDpid, Long srcPortNo, Long dstDpid, Long dstPortNo) {
+		DetachableLinkImpl link = (DetachableLinkImpl)getSwitch(srcDpid).getPort(srcPortNo).getOutgoingLink();
+		if (link.getDstSwitch().getDpid().equals(dstDpid) && link.getDstPort().getNumber().equals(dstPortNo)) {
+			link.detachFromGraph();
+		}
+	}
+}