diff --git a/pregelix-example/src/main/java/edu/uci/ics/pregelix/example/io/VIntWritable.java b/pregelix-example/src/main/java/edu/uci/ics/pregelix/example/io/VIntWritable.java
index a5c9c60..94df74f 100644
--- a/pregelix-example/src/main/java/edu/uci/ics/pregelix/example/io/VIntWritable.java
+++ b/pregelix-example/src/main/java/edu/uci/ics/pregelix/example/io/VIntWritable.java
@@ -42,7 +42,7 @@
     }
 
     public int sizeInBytes() {
-        return 4;
+        return 5;
     }
 
     /** Set the value of this VIntWritable. */
diff --git a/pregelix-example/src/test/java/edu/uci/ics/pregelix/example/lib/io/SizeEstimationTest.java b/pregelix-example/src/test/java/edu/uci/ics/pregelix/example/lib/io/SizeEstimationTest.java
new file mode 100644
index 0000000..196b114
--- /dev/null
+++ b/pregelix-example/src/test/java/edu/uci/ics/pregelix/example/lib/io/SizeEstimationTest.java
@@ -0,0 +1,151 @@
+/*
+ * Copyright 2009-2013 by The Regents of the University of California
+ * 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 from
+ * 
+ *     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 edu.uci.ics.pregelix.example.lib.io;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataOutput;
+import java.io.DataOutputStream;
+import java.util.Random;
+
+import org.junit.Test;
+
+import edu.uci.ics.pregelix.api.graph.MsgList;
+import edu.uci.ics.pregelix.api.io.WritableSizable;
+import edu.uci.ics.pregelix.example.io.BooleanWritable;
+import edu.uci.ics.pregelix.example.io.ByteWritable;
+import edu.uci.ics.pregelix.example.io.DoubleWritable;
+import edu.uci.ics.pregelix.example.io.IntWritable;
+import edu.uci.ics.pregelix.example.io.LongWritable;
+import edu.uci.ics.pregelix.example.io.NullWritable;
+import edu.uci.ics.pregelix.example.io.VIntWritable;
+import edu.uci.ics.pregelix.example.io.VLongWritable;
+
+/**
+ * @author yingyib
+ */
+public class SizeEstimationTest {
+
+    @Test
+    public void testVLong() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new VLongWritable(Math.abs(rand.nextLong())));
+        }
+        verifySizeEstimation(msgList);
+    }
+
+    @Test
+    public void testLong() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new LongWritable(rand.nextLong()));
+        }
+        verifySizeEstimation(msgList);
+    }
+
+    @Test
+    public void testBoolean() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new BooleanWritable(rand.nextBoolean()));
+        }
+        verifySizeEstimation(msgList);
+    }
+
+    @Test
+    public void testByte() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new ByteWritable((byte) rand.nextInt()));
+        }
+        verifySizeEstimation(msgList);
+    }
+
+    @Test
+    public void testDouble() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new DoubleWritable(rand.nextDouble()));
+        }
+        verifySizeEstimation(msgList);
+    }
+
+    @Test
+    public void testFloat() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new DoubleWritable(rand.nextFloat()));
+        }
+        verifySizeEstimation(msgList);
+    }
+    
+    @Test
+    public void testNull() throws Exception {
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(NullWritable.get());
+        }
+        verifySizeEstimation(msgList);
+    }
+    
+    @Test
+    public void testVInt() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new VIntWritable(rand.nextInt()));
+        }
+        verifySizeEstimation(msgList);
+    }
+    
+    @Test
+    public void testInt() throws Exception {
+        Random rand = new Random(System.currentTimeMillis());
+        MsgList<WritableSizable> msgList = new MsgList<WritableSizable>();
+        for (int i = 0; i < 1000000; i++) {
+            msgList.add(new IntWritable(rand.nextInt()));
+        }
+        verifySizeEstimation(msgList);
+    }
+
+    private void verifySizeEstimation(MsgList<WritableSizable> msgList) throws Exception {
+        ByteArrayOutputStream bos = new ByteArrayOutputStream();
+        DataOutput dos = new DataOutputStream(bos);
+        int accumulatedSize = 5;
+        for (int i = 0; i < msgList.size(); i++) {
+            bos.reset();
+            WritableSizable value = msgList.get(i);
+            value.write(dos);
+            if (value.sizeInBytes() < bos.size()) {
+                throw new Exception(value + " estimated size (" + value.sizeInBytes()
+                        + ") is smaller than the actual size" + bos.size());
+            }
+            accumulatedSize += value.sizeInBytes();
+        }
+        bos.reset();
+        msgList.write(dos);
+        if (accumulatedSize < bos.size()) {
+            throw new Exception("Estimated list size (" + accumulatedSize + ") is smaller than the actual size"
+                    + bos.size());
+        }
+    }
+
+}
diff --git a/pregelix-example/src/test/java/edu/uci/ics/pregelix/example/lib/io/VLongWritableTest.java b/pregelix-example/src/test/java/edu/uci/ics/pregelix/example/lib/io/VLongWritableTest.java
deleted file mode 100644
index e2a67f0..0000000
--- a/pregelix-example/src/test/java/edu/uci/ics/pregelix/example/lib/io/VLongWritableTest.java
+++ /dev/null
@@ -1,58 +0,0 @@
-/*
- * Copyright 2009-2013 by The Regents of the University of California
- * 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 from
- * 
- *     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 edu.uci.ics.pregelix.example.lib.io;
-
-import java.io.ByteArrayOutputStream;
-import java.io.DataOutput;
-import java.io.DataOutputStream;
-import java.util.Random;
-
-import org.junit.Test;
-
-import edu.uci.ics.pregelix.api.graph.MsgList;
-import edu.uci.ics.pregelix.example.io.VLongWritable;
-
-/**
- * @author yingyib
- */
-public class VLongWritableTest {
-
-    @Test
-    public void test() throws Exception {
-        ByteArrayOutputStream bos = new ByteArrayOutputStream();
-        DataOutput dos = new DataOutputStream(bos);
-        Random rand = new Random(System.currentTimeMillis());
-        MsgList<VLongWritable> msgList = new MsgList<VLongWritable>();
-        int accumulatedSize = 4;
-        for (int i = 0; i < 1000000; i++) {
-            bos.reset();
-            VLongWritable value = new VLongWritable(Math.abs(rand.nextLong()));
-            value.write(dos);
-            if (value.sizeInBytes() < bos.size()) {
-                throw new Exception(value + " estimated size (" + value.sizeInBytes()
-                        + ") is smaller than the actual size" + bos.size());
-            }
-            msgList.add(value);
-            accumulatedSize += value.sizeInBytes();
-        }
-        bos.reset();
-        msgList.write(dos);
-        if (accumulatedSize < bos.size()) {
-            throw new Exception("Estimated list size (" + accumulatedSize + ") is smaller than the actual size"
-                    + bos.size());
-        }
-    }
-
-}