diff --git a/csharp/src/Google.Protobuf.Test/CodedInputStreamExtensions.cs b/csharp/src/Google.Protobuf.Test/CodedInputStreamExtensions.cs
new file mode 100644
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+++ b/csharp/src/Google.Protobuf.Test/CodedInputStreamExtensions.cs
@@ -0,0 +1,53 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 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.
+#endregion
+
+using NUnit.Framework;
+
+namespace Google.Protobuf
+{
+    internal static class CodedInputStreamExtensions
+    {
+        public static void AssertNextTag(this CodedInputStream input, uint expectedTag)
+        {
+            uint tag = input.ReadTag();
+            Assert.AreEqual(expectedTag, tag);
+        }
+
+        public static T ReadMessage<T>(this CodedInputStream stream, MessageParser<T> parser)
+            where T : IMessage<T>
+        {
+            var message = parser.CreateTemplate();
+            stream.ReadMessage(message);
+            return message;
+        }
+    }
+}