added tests.

Author: zhumin8

gax-java/gax/src/main/java/com/google/api/gax/logging/Slf4jUtils.java

@@ -102,7 +102,6 @@ static void logWithMDC(
       for (Entry<String, Object> entry : contextMap.entrySet()) {
         String key = entry.getKey();
         Object value = entry.getValue();
-        // MDC.put(key, value.toString());
         MDC.put(key, value instanceof String ? (String) value : gson.toJson(value));
       }
     }

gax-java/gax/src/test/java/com/google/api/gax/logging/Slf4jUtilsTest.java

@@ -100,6 +100,38 @@ void testLogWithMDC_InfoLevel_VerifyMDC() {
     assertEquals(message, testLogger.messageList.get(0));
   }
 
+  @Test
+  void testLogWithMDC_DEBUG() {
+    TestLogger testLogger = new TestLogger("test-logger");
+    Slf4jUtils.logWithMDC(testLogger, Level.DEBUG, new HashMap<>(), "test message");
+
+    assertEquals(Level.DEBUG, testLogger.level);
+  }
+
+  @Test
+  void testLogWithMDC_TRACE() {
+    TestLogger testLogger = new TestLogger("test-logger");
+    Slf4jUtils.logWithMDC(testLogger, Level.TRACE, new HashMap<>(), "test message");
+
+    assertEquals(Level.TRACE, testLogger.level);
+  }
+
+  @Test
+  void testLogWithMDC_WARN() {
+    TestLogger testLogger = new TestLogger("test-logger");
+    Slf4jUtils.logWithMDC(testLogger, Level.WARN, new HashMap<>(), "test message");
+
+    assertEquals(Level.WARN, testLogger.level);
+  }
+
+  @Test
+  void testLogWithMDC_ERROR() {
+    TestLogger testLogger = new TestLogger("test-logger");
+    Slf4jUtils.logWithMDC(testLogger, Level.ERROR, new HashMap<>(), "test message");
+
+    assertEquals(Level.ERROR, testLogger.level);
+  }
+
   @Test
   void testMessageToMap_ValidMessage() throws InvalidProtocolBufferException {
     Field field =

gax-java/gax/src/test/java/com/google/api/gax/logging/TestLogger.java

@@ -77,7 +77,9 @@ public boolean isTraceEnabled() {
   }
 
   @Override
-  public void trace(String msg) {}
+  public void trace(String msg) {
+    level = Level.TRACE;
+  }
 
   @Override
   public void trace(String format, Object arg) {}
@@ -121,6 +123,7 @@ public void debug(String msg) {
     Map<String, String> currentMDC = MDC.getCopyOfContextMap();
     MDCMap.putAll(currentMDC);
     messageList.add(msg);
+    level = Level.DEBUG;
   }
 
   @Override
@@ -208,7 +211,9 @@ public boolean isWarnEnabled() {
   }
 
   @Override
-  public void warn(String msg) {}
+  public void warn(String msg) {
+    level = Level.WARN;
+  }
 
   @Override
   public void warn(String format, Object arg) {}
@@ -248,7 +253,9 @@ public boolean isErrorEnabled() {
   }
 
   @Override
-  public void error(String msg) {}
+  public void error(String msg) {
+    level = Level.ERROR;
+  }
 
   @Override
   public void error(String format, Object arg) {}