diff --git a/pom.xml b/pom.xml
index 7f544d500..27c504924 100644
--- a/pom.xml
+++ b/pom.xml
@@ -155,6 +155,7 @@
                     <instrumentation>
                         <excludes>
                             <exclude>com/a/eye/skywalking/trace/proto/*.class</exclude>
+                            <exclude>com/a/eye/skywalking/sniffer/mock/**/*.class</exclude>
                         </excludes>
                     </instrumentation>
                 </configuration>
diff --git a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/EasyLogger.java b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/EasyLogger.java
index e449fbf0a..ac8ee73b8 100644
--- a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/EasyLogger.java
+++ b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/EasyLogger.java
@@ -1,7 +1,6 @@
 package com.a.eye.skywalking.api.logging;
 
 
-import com.a.eye.skywalking.api.util.LoggingUtil;
 import java.net.URLEncoder;
 import java.text.SimpleDateFormat;
 import java.util.Date;
@@ -32,7 +31,7 @@ public class EasyLogger implements ILog {
         }
 
         if (e != null) {
-            WriterFactory.getLogWriter().writeError(LoggingUtil.fetchThrowableStack(e));
+            WriterFactory.getLogWriter().writeError(ThrowableFormatter.format(e));
         }
     }
 
diff --git a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/SyncFileWriter.java b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/SyncFileWriter.java
index 579e098ba..99d081143 100644
--- a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/SyncFileWriter.java
+++ b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/SyncFileWriter.java
@@ -3,7 +3,6 @@ package com.a.eye.skywalking.api.logging;
 
 
 import com.a.eye.skywalking.api.conf.Config;
-import com.a.eye.skywalking.api.util.LoggingUtil;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
@@ -97,15 +96,15 @@ public class SyncFileWriter implements IWriter {
         try {
             File file = new File(Config.Logging.LOG_DIR_NAME, Config.Logging.SYSTEM_ERROR_LOG_FILE_NAME);
             fileOutputStream = new FileOutputStream(file, true);
-            fileOutputStream.write(("Failed to init sync File Writer.\n" + LoggingUtil.fetchThrowableStack(e)).getBytes());
+            fileOutputStream.write(("Failed to init sync File Writer.\n" + ThrowableFormatter.format(e)).getBytes());
         } catch (Exception e1) {
-            System.err.print(LoggingUtil.fetchThrowableStack(e1));
+            System.err.print(ThrowableFormatter.format(e1));
         } finally {
             if (fileOutputStream != null) {
                 try {
                     fileOutputStream.close();
                 } catch (IOException e1) {
-                    System.err.print(LoggingUtil.fetchThrowableStack(e1));
+                    System.err.print(ThrowableFormatter.format(e1));
                 }
             }
         }
diff --git a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/util/LoggingUtil.java b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/ThrowableFormatter.java
similarity index 80%
rename from skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/util/LoggingUtil.java
rename to skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/ThrowableFormatter.java
index dbfc3102c..429e63d49 100644
--- a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/util/LoggingUtil.java
+++ b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/logging/ThrowableFormatter.java
@@ -1,4 +1,4 @@
-package com.a.eye.skywalking.api.util;
+package com.a.eye.skywalking.api.logging;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -6,8 +6,8 @@ import java.io.IOException;
 /**
  * Created by xin on 16-6-24.
  */
-public class LoggingUtil {
-    public static String fetchThrowableStack(Throwable e) {
+public class ThrowableFormatter {
+    public static String format(Throwable e) {
         ByteArrayOutputStream buf = new ByteArrayOutputStream();
         e.printStackTrace(new java.io.PrintWriter(buf, true));
         String expMessage = buf.toString();
diff --git a/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/logging/STDOutWriterTest.java b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/logging/STDOutWriterTest.java
new file mode 100644
index 000000000..31a5c2a54
--- /dev/null
+++ b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/logging/STDOutWriterTest.java
@@ -0,0 +1,52 @@
+package com.a.eye.skywalking.api.logging;
+
+import java.io.PrintStream;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Mockito.times;
+
+/**
+ * Created by wusheng on 2017/2/28.
+ */
+public class STDOutWriterTest {
+    private static PrintStream outRef;
+    private static PrintStream errRef;
+
+    @BeforeClass
+    public static void initAndHoldOut(){
+        outRef = System.out;
+        errRef = System.err;
+    }
+
+    @Test
+    public void testWrite(){
+        PrintStream mockStream = Mockito.mock(PrintStream.class);
+        System.setOut(mockStream);
+
+        STDOutWriter writer = new STDOutWriter();
+        writer.write("hello");
+
+        Mockito.verify(mockStream,times(1)).println(anyString());
+    }
+
+    @Test
+    public void testWriteError(){
+        PrintStream mockStream = Mockito.mock(PrintStream.class);
+        System.setErr(mockStream);
+
+        STDOutWriter writer = new STDOutWriter();
+        writer.writeError("hello");
+
+        Mockito.verify(mockStream,times(1)).println(anyString());
+    }
+
+    @AfterClass
+    public static void reset(){
+        System.setOut(outRef);
+        System.setErr(errRef);
+    }
+}
diff --git a/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/logging/ThrowableFormatterTest.java b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/logging/ThrowableFormatterTest.java
new file mode 100644
index 000000000..048b2ae5f
--- /dev/null
+++ b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/logging/ThrowableFormatterTest.java
@@ -0,0 +1,18 @@
+package com.a.eye.skywalking.api.logging;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Created by wusheng on 2017/2/28.
+ */
+public class ThrowableFormatterTest {
+    @Test
+    public void testFormat(){
+        NullPointerException exception = new NullPointerException();
+        String formatLines = ThrowableFormatter.format(exception);
+        String[] lines = formatLines.split("\n");
+        Assert.assertEquals("java.lang.NullPointerException", lines[0]);
+        Assert.assertEquals("\tat com.a.eye.skywalking.api.logging.ThrowableFormatterTest.testFormat(ThrowableFormatterTest.java:12)", lines[1]);
+    }
+}
diff --git a/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/plugin/bytebuddy/AllObjectDefaultMethodsMatchTest.java b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/plugin/bytebuddy/AllObjectDefaultMethodsMatchTest.java
new file mode 100644
index 000000000..091190871
--- /dev/null
+++ b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/plugin/bytebuddy/AllObjectDefaultMethodsMatchTest.java
@@ -0,0 +1,12 @@
+package com.a.eye.skywalking.api.plugin.bytebuddy;
+
+import org.junit.Test;
+
+/**
+ * Created by wusheng on 2017/2/28.
+ */
+public class AllObjectDefaultMethodsMatchTest {
+    @Test
+    public void testMatches(){
+    }
+}