Mock Networkstream.Read

Question

I've been trying to mock a network stream for some unit tests.

So far, using Moq the best I've come up with is to use a wrapper for the stream and then mock my interface.

public interface INetworkstreamWrapper
{
    int Read(byte[] buffer, int offset,int size);

    void Flush();

    bool DataAvailable { get; }

    bool CanRead { get; }

    void close();
}

Question is, whilst that gives me a start, I actually want to test some byte array values as read into my read buffer. How can I return some test data into the buffer when calling Read() on the mock object?

Answer 1

You can use a callback to gain access to the passed parameter and alter them:

public void TestRead()
{
  var streamMock = new Mock<INetworkstreamWrapper>();

   streamMock
            .Setup(m => m.Read(It.IsAny<byte[]>(), 
                               It.IsAny<int>(), 
                               It.IsAny<int>()))
            .Callback((byte[] buffer, int offset, int size) => buffer[0] = 128);

   var myBuffer = new byte[10];
   streamMock.Object.Read(myBuffer,0,10);

   Assert.AreEqual(128, myBuffer[0]);
}

But I would suggest you rethink your strategy about that kind of mocking, see: http://davesquared.net/2011/04/dont-mock-types-you-dont-own.html

Maybe you could write an integration test instead, or make your code depend on the abstract Stream class.

In your test you could then use a MemoryStream to check your class correct behaviour when fetching data from the Stream.