diff --git a/js/proto3_test.js b/js/proto3_test.js
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+++ b/js/proto3_test.js
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+// 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.require('goog.testing.asserts');
+goog.require('proto.jspb.test.ForeignMessage');
+goog.require('proto.jspb.test.Proto3Enum');
+goog.require('proto.jspb.test.TestProto3');
+
+/**
+ * Helper: compare a bytes field to a string with codepoints 0--255.
+ * @param {Uint8Array|string} arr
+ * @param {string} str
+ * @return {boolean}
+ */
+function bytesCompare(arr, str) {
+  if (arr.length != str.length) {
+    return false;
+  }
+  if (typeof arr == 'string') {
+    for (var i = 0; i < arr.length; i++) {
+      if (arr.charCodeAt(i) != str.charCodeAt(i)) {
+        return false;
+      }
+    }
+    return true;
+  } else {
+    for (var i = 0; i < arr.length; i++) {
+      if (arr[i] != str.charCodeAt(i)) {
+        return false;
+      }
+    }
+    return true;
+  }
+}
+
+
+describe('proto3Test', function() {
+  /**
+   * Test defaults for proto3 message fields.
+   */
+  it('testProto3FieldDefaults', function() {
+    var msg = new proto.jspb.test.TestProto3();
+
+    assertEquals(msg.getOptionalInt32(), 0);
+    assertEquals(msg.getOptionalInt64(), 0);
+    assertEquals(msg.getOptionalUint32(), 0);
+    assertEquals(msg.getOptionalUint64(), 0);
+    assertEquals(msg.getOptionalSint32(), 0);
+    assertEquals(msg.getOptionalSint64(), 0);
+    assertEquals(msg.getOptionalFixed32(), 0);
+    assertEquals(msg.getOptionalFixed64(), 0);
+    assertEquals(msg.getOptionalSfixed32(), 0);
+    assertEquals(msg.getOptionalSfixed64(), 0);
+    assertEquals(msg.getOptionalFloat(), 0);
+    assertEquals(msg.getOptionalDouble(), 0);
+    assertEquals(msg.getOptionalString(), '');
+
+    // If/when we change bytes fields to return Uint8Array, we'll want to switch
+    // to this assertion instead:
+    //assertEquals(msg.getOptionalBytes() instanceof Uint8Array, true);
+    assertEquals(typeof msg.getOptionalBytes(), 'string');
+
+    assertEquals(msg.getOptionalBytes().length, 0);
+    assertEquals(msg.getOptionalForeignEnum(), proto.jspb.test.Proto3Enum.PROTO3_FOO);
+    assertEquals(msg.getOptionalForeignMessage(), undefined);
+    assertEquals(msg.getOptionalForeignMessage(), undefined);
+
+    assertEquals(msg.getRepeatedInt32List().length, 0);
+    assertEquals(msg.getRepeatedInt64List().length, 0);
+    assertEquals(msg.getRepeatedUint32List().length, 0);
+    assertEquals(msg.getRepeatedUint64List().length, 0);
+    assertEquals(msg.getRepeatedSint32List().length, 0);
+    assertEquals(msg.getRepeatedSint64List().length, 0);
+    assertEquals(msg.getRepeatedFixed32List().length, 0);
+    assertEquals(msg.getRepeatedFixed64List().length, 0);
+    assertEquals(msg.getRepeatedSfixed32List().length, 0);
+    assertEquals(msg.getRepeatedSfixed64List().length, 0);
+    assertEquals(msg.getRepeatedFloatList().length, 0);
+    assertEquals(msg.getRepeatedDoubleList().length, 0);
+    assertEquals(msg.getRepeatedStringList().length, 0);
+    assertEquals(msg.getRepeatedBytesList().length, 0);
+    assertEquals(msg.getRepeatedForeignEnumList().length, 0);
+    assertEquals(msg.getRepeatedForeignMessageList().length, 0);
+
+  });
+
+
+  /**
+   * Test that all fields can be set and read via a serialization roundtrip.
+   */
+  it('testProto3FieldSetGet', function() {
+    var msg = new proto.jspb.test.TestProto3();
+
+    msg.setOptionalInt32(-42);
+    msg.setOptionalInt64(-0x7fffffff00000000);
+    msg.setOptionalUint32(0x80000000);
+    msg.setOptionalUint64(0xf000000000000000);
+    msg.setOptionalSint32(-100);
+    msg.setOptionalSint64(-0x8000000000000000);
+    msg.setOptionalFixed32(1234);
+    msg.setOptionalFixed64(0x1234567800000000);
+    msg.setOptionalSfixed32(-1234);
+    msg.setOptionalSfixed64(-0x1234567800000000);
+    msg.setOptionalFloat(1.5);
+    msg.setOptionalDouble(-1.5);
+    msg.setOptionalBool(true);
+    msg.setOptionalString('hello world');
+    msg.setOptionalBytes('bytes');
+    var submsg = new proto.jspb.test.ForeignMessage();
+    submsg.setC(16);
+    msg.setOptionalForeignMessage(submsg);
+    msg.setOptionalForeignEnum(proto.jspb.test.Proto3Enum.PROTO3_BAR);
+
+    msg.setRepeatedInt32List([-42]);
+    msg.setRepeatedInt64List([-0x7fffffff00000000]);
+    msg.setRepeatedUint32List([0x80000000]);
+    msg.setRepeatedUint64List([0xf000000000000000]);
+    msg.setRepeatedSint32List([-100]);
+    msg.setRepeatedSint64List([-0x8000000000000000]);
+    msg.setRepeatedFixed32List([1234]);
+    msg.setRepeatedFixed64List([0x1234567800000000]);
+    msg.setRepeatedSfixed32List([-1234]);
+    msg.setRepeatedSfixed64List([-0x1234567800000000]);
+    msg.setRepeatedFloatList([1.5]);
+    msg.setRepeatedDoubleList([-1.5]);
+    msg.setRepeatedBoolList([true]);
+    msg.setRepeatedStringList(['hello world']);
+    msg.setRepeatedBytesList(['bytes']);
+    submsg = new proto.jspb.test.ForeignMessage();
+    submsg.setC(1000);
+    msg.setRepeatedForeignMessageList([submsg]);
+    msg.setRepeatedForeignEnumList([proto.jspb.test.Proto3Enum.PROTO3_BAR]);
+
+    msg.setOneofString('asdf');
+
+    var serialized = msg.serializeBinary();
+    msg = proto.jspb.test.TestProto3.deserializeBinary(serialized);
+
+    assertEquals(msg.getOptionalInt32(), -42);
+    assertEquals(msg.getOptionalInt64(), -0x7fffffff00000000);
+    assertEquals(msg.getOptionalUint32(), 0x80000000);
+    assertEquals(msg.getOptionalUint64(), 0xf000000000000000);
+    assertEquals(msg.getOptionalSint32(), -100);
+    assertEquals(msg.getOptionalSint64(), -0x8000000000000000);
+    assertEquals(msg.getOptionalFixed32(), 1234);
+    assertEquals(msg.getOptionalFixed64(), 0x1234567800000000);
+    assertEquals(msg.getOptionalSfixed32(), -1234);
+    assertEquals(msg.getOptionalSfixed64(), -0x1234567800000000);
+    assertEquals(msg.getOptionalFloat(), 1.5);
+    assertEquals(msg.getOptionalDouble(), -1.5);
+    assertEquals(msg.getOptionalBool(), true);
+    assertEquals(msg.getOptionalString(), 'hello world');
+    assertEquals(true, bytesCompare(msg.getOptionalBytes(), 'bytes'));
+    assertEquals(msg.getOptionalForeignMessage().getC(), 16);
+    assertEquals(msg.getOptionalForeignEnum(),
+        proto.jspb.test.Proto3Enum.PROTO3_BAR);
+
+    assertElementsEquals(msg.getRepeatedInt32List(), [-42]);
+    assertElementsEquals(msg.getRepeatedInt64List(), [-0x7fffffff00000000]);
+    assertElementsEquals(msg.getRepeatedUint32List(), [0x80000000]);
+    assertElementsEquals(msg.getRepeatedUint64List(), [0xf000000000000000]);
+    assertElementsEquals(msg.getRepeatedSint32List(), [-100]);
+    assertElementsEquals(msg.getRepeatedSint64List(), [-0x8000000000000000]);
+    assertElementsEquals(msg.getRepeatedFixed32List(), [1234]);
+    assertElementsEquals(msg.getRepeatedFixed64List(), [0x1234567800000000]);
+    assertElementsEquals(msg.getRepeatedSfixed32List(), [-1234]);
+    assertElementsEquals(msg.getRepeatedSfixed64List(), [-0x1234567800000000]);
+    assertElementsEquals(msg.getRepeatedFloatList(), [1.5]);
+    assertElementsEquals(msg.getRepeatedDoubleList(), [-1.5]);
+    assertElementsEquals(msg.getRepeatedBoolList(), [true]);
+    assertElementsEquals(msg.getRepeatedStringList(), ['hello world']);
+    assertEquals(msg.getRepeatedBytesList().length, 1);
+    assertEquals(true, bytesCompare(msg.getRepeatedBytesList()[0], 'bytes'));
+    assertEquals(msg.getRepeatedForeignMessageList().length, 1);
+    assertEquals(msg.getRepeatedForeignMessageList()[0].getC(), 1000);
+    assertElementsEquals(msg.getRepeatedForeignEnumList(),
+        [proto.jspb.test.Proto3Enum.PROTO3_BAR]);
+
+    assertEquals(msg.getOneofString(), 'asdf');
+  });
+
+
+  /**
+   * Test that oneofs continue to have a notion of field presence.
+   */
+  it('testOneofs', function() {
+    var msg = new proto.jspb.test.TestProto3();
+
+    assertEquals(msg.getOneofUint32(), undefined);
+    assertEquals(msg.getOneofForeignMessage(), undefined);
+    assertEquals(msg.getOneofString(), undefined);
+    assertEquals(msg.getOneofBytes(), undefined);
+
+    msg.setOneofUint32(42);
+    assertEquals(msg.getOneofUint32(), 42);
+    assertEquals(msg.getOneofForeignMessage(), undefined);
+    assertEquals(msg.getOneofString(), undefined);
+    assertEquals(msg.getOneofBytes(), undefined);
+
+
+    var submsg = new proto.jspb.test.ForeignMessage();
+    msg.setOneofForeignMessage(submsg);
+    assertEquals(msg.getOneofUint32(), undefined);
+    assertEquals(msg.getOneofForeignMessage(), submsg);
+    assertEquals(msg.getOneofString(), undefined);
+    assertEquals(msg.getOneofBytes(), undefined);
+
+    msg.setOneofString('hello');
+    assertEquals(msg.getOneofUint32(), undefined);
+    assertEquals(msg.getOneofForeignMessage(), undefined);
+    assertEquals(msg.getOneofString(), 'hello');
+    assertEquals(msg.getOneofBytes(), undefined);
+
+    msg.setOneofBytes('\u00FF\u00FF');
+    assertEquals(msg.getOneofUint32(), undefined);
+    assertEquals(msg.getOneofForeignMessage(), undefined);
+    assertEquals(msg.getOneofString(), undefined);
+    assertEquals(msg.getOneofBytes(), '\u00FF\u00FF');
+  });
+
+
+  /**
+   * Test that "default"-valued primitive fields are not emitted on the wire.
+   */
+  it('testNoSerializeDefaults', function() {
+    var msg = new proto.jspb.test.TestProto3();
+
+    // Set each primitive to a non-default value, then back to its default, to
+    // ensure that the serialization is actually checking the value and not just
+    // whether it has ever been set.
+    msg.setOptionalInt32(42);
+    msg.setOptionalInt32(0);
+    msg.setOptionalDouble(3.14);
+    msg.setOptionalDouble(0.0);
+    msg.setOptionalBool(true);
+    msg.setOptionalBool(false);
+    msg.setOptionalString('hello world');
+    msg.setOptionalString('');
+    msg.setOptionalBytes('\u00FF\u00FF');
+    msg.setOptionalBytes('');
+    msg.setOptionalForeignMessage(new proto.jspb.test.ForeignMessage());
+    msg.setOptionalForeignMessage(null);
+    msg.setOptionalForeignEnum(proto.jspb.test.Proto3Enum.PROTO3_BAR);
+    msg.setOptionalForeignEnum(proto.jspb.test.Proto3Enum.PROTO3_FOO);
+    msg.setOneofUint32(32);
+    msg.setOneofUint32(null);
+
+
+    var serialized = msg.serializeBinary();
+    assertEquals(0, serialized.length);
+  });
+});