Simulating a Server in .Net (C#)

I recently had a need to simulate an FTP server connection in some unit tests. Rather than developing a full test-server, for this purpose, I could easily simulate an FTP stream by creating it in memory, and then passing that stream to the functions  that expect it:

        public Stream CreateTestStream(string text)
        {
            byte[] buff = Encoding.ASCII.GetBytes(text);
            return new MemoryStream(buff, false);
        }

This function merely accepts text (FTP is text-based after all), and returns a memory stream. I can then use it in a unit test:

[Test]
        [ExpectedException(typeof(FtpException),"InvalidResponse")]
        public void FtpResponse_Constructor_BadStream_InvalidCode()
        {
            using (Stream s = CreateTestStream("NoErrorCode"))
            {
                FtpResponse response = new FtpResponse(s);
            }
        }