Testing and related fixes
diff --git a/src/ProtocolBuffers.Test/ExtendableMessageTest.cs b/src/ProtocolBuffers.Test/ExtendableMessageTest.cs
new file mode 100644
index 0000000..ab04ef0
--- /dev/null
+++ b/src/ProtocolBuffers.Test/ExtendableMessageTest.cs
@@ -0,0 +1,187 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://github.com/jskeet/dotnet-protobufs/
+// Original C++/Java/Python code:
+// http://code.google.com/p/protobuf/
+//
+// 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.
+#endregion
+
+using System;
+using System.Collections.Generic;
+using Google.ProtocolBuffers;
+using Google.ProtocolBuffers.TestProtos;
+using NUnit.Framework;
+
+namespace Google.ProtocolBuffers {
+  [TestFixture]
+  public class ExtendableMessageTest {
+
+
+    [Test]
+    public void ExtensionWriterTest() {
+      TestAllExtensions.Builder builder = TestAllExtensions.CreateBuilder()
+        .SetExtension(UnitTestProtoFile.DefaultBoolExtension, true)
+        .SetExtension(UnitTestProtoFile.DefaultBytesExtension, ByteString.CopyFromUtf8("123"))
+        .SetExtension(UnitTestProtoFile.DefaultCordExtension, "123")
+        .SetExtension(UnitTestProtoFile.DefaultDoubleExtension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultFixed32Extension, 123u)
+        .SetExtension(UnitTestProtoFile.DefaultFixed64Extension, 123u)
+        .SetExtension(UnitTestProtoFile.DefaultFloatExtension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultForeignEnumExtension, ForeignEnum.FOREIGN_BAZ)
+        .SetExtension(UnitTestProtoFile.DefaultImportEnumExtension, ImportEnum.IMPORT_BAZ)
+        .SetExtension(UnitTestProtoFile.DefaultInt32Extension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultInt64Extension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultNestedEnumExtension, TestAllTypes.Types.NestedEnum.FOO)
+        .SetExtension(UnitTestProtoFile.DefaultSfixed32Extension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultSfixed64Extension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultSint32Extension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultSint64Extension, 123)
+        .SetExtension(UnitTestProtoFile.DefaultStringExtension, "123")
+        .SetExtension(UnitTestProtoFile.DefaultStringPieceExtension, "123")
+        .SetExtension(UnitTestProtoFile.DefaultUint32Extension, 123u)
+        .SetExtension(UnitTestProtoFile.DefaultUint64Extension, 123u)
+        //Optional
+        .SetExtension(UnitTestProtoFile.OptionalBoolExtension, true)
+        .SetExtension(UnitTestProtoFile.OptionalBytesExtension, ByteString.CopyFromUtf8("123"))
+        .SetExtension(UnitTestProtoFile.OptionalCordExtension, "123")
+        .SetExtension(UnitTestProtoFile.OptionalDoubleExtension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalFixed32Extension, 123u)
+        .SetExtension(UnitTestProtoFile.OptionalFixed64Extension, 123u)
+        .SetExtension(UnitTestProtoFile.OptionalFloatExtension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalForeignEnumExtension, ForeignEnum.FOREIGN_BAZ)
+        .SetExtension(UnitTestProtoFile.OptionalImportEnumExtension, ImportEnum.IMPORT_BAZ)
+        .SetExtension(UnitTestProtoFile.OptionalInt32Extension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalInt64Extension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalNestedEnumExtension, TestAllTypes.Types.NestedEnum.FOO)
+        .SetExtension(UnitTestProtoFile.OptionalSfixed32Extension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalSfixed64Extension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalSint32Extension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalSint64Extension, 123)
+        .SetExtension(UnitTestProtoFile.OptionalStringExtension, "123")
+        .SetExtension(UnitTestProtoFile.OptionalStringPieceExtension, "123")
+        .SetExtension(UnitTestProtoFile.OptionalUint32Extension, 123u)
+        .SetExtension(UnitTestProtoFile.OptionalUint64Extension, 123u)
+        //Repeated
+        .AddExtension(UnitTestProtoFile.RepeatedBoolExtension, true)
+        .AddExtension(UnitTestProtoFile.RepeatedBytesExtension, ByteString.CopyFromUtf8("123"))
+        .AddExtension(UnitTestProtoFile.RepeatedCordExtension, "123")
+        .AddExtension(UnitTestProtoFile.RepeatedDoubleExtension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedFixed32Extension, 123u)
+        .AddExtension(UnitTestProtoFile.RepeatedFixed64Extension, 123u)
+        .AddExtension(UnitTestProtoFile.RepeatedFloatExtension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedForeignEnumExtension, ForeignEnum.FOREIGN_BAZ)
+        .AddExtension(UnitTestProtoFile.RepeatedImportEnumExtension, ImportEnum.IMPORT_BAZ)
+        .AddExtension(UnitTestProtoFile.RepeatedInt32Extension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedInt64Extension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedNestedEnumExtension, TestAllTypes.Types.NestedEnum.FOO)
+        .AddExtension(UnitTestProtoFile.RepeatedSfixed32Extension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedSfixed64Extension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedSint32Extension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedSint64Extension, 123)
+        .AddExtension(UnitTestProtoFile.RepeatedStringExtension, "123")
+        .AddExtension(UnitTestProtoFile.RepeatedStringPieceExtension, "123")
+        .AddExtension(UnitTestProtoFile.RepeatedUint32Extension, 123u)
+        .AddExtension(UnitTestProtoFile.RepeatedUint64Extension, 123u)
+        ;
+      TestAllExtensions msg = builder.Build();
+
+      ExtensionRegistry registry = ExtensionRegistry.CreateInstance();
+      UnitTestProtoFile.RegisterAllExtensions(registry);
+
+      TestAllExtensions.Builder copyBuilder = TestAllExtensions.CreateBuilder().MergeFrom(msg.ToByteArray(), registry);
+      TestAllExtensions copy = copyBuilder.Build();
+
+      Assert.AreEqual(msg.ToByteArray(), copy.ToByteArray());
+
+      Assert.AreEqual(true, copy.GetExtension(UnitTestProtoFile.DefaultBoolExtension));
+      Assert.AreEqual(ByteString.CopyFromUtf8("123"), copy.GetExtension(UnitTestProtoFile.DefaultBytesExtension));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.DefaultCordExtension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultDoubleExtension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.DefaultFixed32Extension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.DefaultFixed64Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultFloatExtension));
+      Assert.AreEqual(ForeignEnum.FOREIGN_BAZ, copy.GetExtension(UnitTestProtoFile.DefaultForeignEnumExtension));
+      Assert.AreEqual(ImportEnum.IMPORT_BAZ, copy.GetExtension(UnitTestProtoFile.DefaultImportEnumExtension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultInt32Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultInt64Extension));
+      Assert.AreEqual(TestAllTypes.Types.NestedEnum.FOO, copy.GetExtension(UnitTestProtoFile.DefaultNestedEnumExtension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultSfixed32Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultSfixed64Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultSint32Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.DefaultSint64Extension));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.DefaultStringExtension));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.DefaultStringPieceExtension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.DefaultUint32Extension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.DefaultUint64Extension));
+
+      Assert.AreEqual(true, copy.GetExtension(UnitTestProtoFile.OptionalBoolExtension));
+      Assert.AreEqual(ByteString.CopyFromUtf8("123"), copy.GetExtension(UnitTestProtoFile.OptionalBytesExtension));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.OptionalCordExtension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalDoubleExtension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.OptionalFixed32Extension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.OptionalFixed64Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalFloatExtension));
+      Assert.AreEqual(ForeignEnum.FOREIGN_BAZ, copy.GetExtension(UnitTestProtoFile.OptionalForeignEnumExtension));
+      Assert.AreEqual(ImportEnum.IMPORT_BAZ, copy.GetExtension(UnitTestProtoFile.OptionalImportEnumExtension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalInt32Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalInt64Extension));
+      Assert.AreEqual(TestAllTypes.Types.NestedEnum.FOO, copy.GetExtension(UnitTestProtoFile.OptionalNestedEnumExtension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalSfixed32Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalSfixed64Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalSint32Extension));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.OptionalSint64Extension));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.OptionalStringExtension));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.OptionalStringPieceExtension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.OptionalUint32Extension));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.OptionalUint64Extension));
+
+      Assert.AreEqual(true, copy.GetExtension(UnitTestProtoFile.RepeatedBoolExtension, 0));
+      Assert.AreEqual(ByteString.CopyFromUtf8("123"), copy.GetExtension(UnitTestProtoFile.RepeatedBytesExtension, 0));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.RepeatedCordExtension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedDoubleExtension, 0));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.RepeatedFixed32Extension, 0));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.RepeatedFixed64Extension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedFloatExtension, 0));
+      Assert.AreEqual(ForeignEnum.FOREIGN_BAZ, copy.GetExtension(UnitTestProtoFile.RepeatedForeignEnumExtension, 0));
+      Assert.AreEqual(ImportEnum.IMPORT_BAZ, copy.GetExtension(UnitTestProtoFile.RepeatedImportEnumExtension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedInt32Extension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedInt64Extension, 0));
+      Assert.AreEqual(TestAllTypes.Types.NestedEnum.FOO, copy.GetExtension(UnitTestProtoFile.RepeatedNestedEnumExtension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedSfixed32Extension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedSfixed64Extension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedSint32Extension, 0));
+      Assert.AreEqual(123, copy.GetExtension(UnitTestProtoFile.RepeatedSint64Extension, 0));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.RepeatedStringExtension, 0));
+      Assert.AreEqual("123", copy.GetExtension(UnitTestProtoFile.RepeatedStringPieceExtension, 0));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.RepeatedUint32Extension, 0));
+      Assert.AreEqual(123u, copy.GetExtension(UnitTestProtoFile.RepeatedUint64Extension, 0));
+    }
+
+  }
+}