diff --git a/js/debug_test.js b/js/debug_test.js
new file mode 100644
index 0000000..615fc7c
--- /dev/null
+++ b/js/debug_test.js
@@ -0,0 +1,101 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+goog.setTestOnly();
+
+goog.require('goog.testing.asserts');
+goog.require('jspb.debug');
+goog.require('proto.jspb.test.HasExtensions');
+goog.require('proto.jspb.test.IsExtension');
+goog.require('proto.jspb.test.Simple1');
+
+
+
+describe('debugTest', function() {
+  it('testSimple1', function() {
+    if (COMPILED) {
+      return;
+    }
+    var message = new proto.jspb.test.Simple1();
+    message.setAString('foo');
+    assertObjectEquals({
+      $name: 'proto.jspb.test.Simple1',
+      'aString': 'foo',
+      'aRepeatedStringList': []
+    }, jspb.debug.dump(message));
+
+    message.setABoolean(true);
+    message.setARepeatedStringList(['1', '2']);
+
+    assertObjectEquals({
+      $name: 'proto.jspb.test.Simple1',
+      'aString': 'foo',
+      'aRepeatedStringList': ['1', '2'],
+      'aBoolean': true
+    }, jspb.debug.dump(message));
+
+    message.setAString(undefined);
+
+    assertObjectEquals({
+      $name: 'proto.jspb.test.Simple1',
+      'aRepeatedStringList': ['1', '2'],
+      'aBoolean': true
+    }, jspb.debug.dump(message));
+  });
+
+
+  it('testExtensions', function() {
+    if (COMPILED) {
+      return;
+    }
+    var extension = new proto.jspb.test.IsExtension();
+    extension.setExt1('ext1field');
+    var extendable = new proto.jspb.test.HasExtensions();
+    extendable.setStr1('v1');
+    extendable.setStr2('v2');
+    extendable.setStr3('v3');
+    extendable.setExtension(proto.jspb.test.IsExtension.extField, extension);
+
+    assertObjectEquals({
+      '$name': 'proto.jspb.test.HasExtensions',
+      'str1': 'v1',
+      'str2': 'v2',
+      'str3': 'v3',
+      '$extensions': {
+        'extField': {
+          '$name': 'proto.jspb.test.IsExtension',
+          'ext1': 'ext1field'
+        },
+        'repeatedSimpleList': []
+      }
+    }, jspb.debug.dump(extendable));
+  });
+
+});