Question

I have a Transfer class, simplified it looks like this:

public class Transfer
{
    public virtual IFileConnection source { get; set; }
    public virtual IFileConnection destination { get; set; }

    public virtual void GetFile(IFileConnection connection, 
        string remoteFilename, string localFilename)
    {
        connection.Get(remoteFilename, localFilename);
    }

    public virtual void PutFile(IFileConnection connection, 
        string localFilename, string remoteFilename)
    {
        connection.Get(remoteFilename, localFilename);
    }

    public virtual void TransferFiles(string sourceName, string destName)
    {
        source = internalConfig.GetFileConnection("source");
        destination = internalConfig.GetFileConnection("destination");
        var tempName = Path.GetTempFileName();
        GetFile(source, sourceName, tempName);
        PutFile(destination, tempName, destName);
    }
}

The simplified version of the IFileConnection interface looks like this:

public interface IFileConnection
{
    void Get(string remoteFileName, string localFileName);
    void Put(string localFileName, string remoteFileName);
}

The real class is supposed to handle a System.IO.IOException that is thrown when the IFileConnection concrete classes loses connectivity with the remote, sending out emails and what not.

I would like to use Moq to create a Transfer class, and use it as my concrete Transfer class in all properties and methods, except when the GetFile method is invoked – then I want it to throw a System.IO.IOException and make sure the Transfer class handles it properly.

Am I using the right tool for the job? Am I going about this the right way? And how would I write the setup for that unit test for NUnit?

Answer 1

This is how I managed to do what I was trying to do:

[Test]
public void TransferHandlesDisconnect()
{
    // ... set up config here
    var methodTester = new Mock<Transfer>(configInfo);
    methodTester.CallBase = true;
    methodTester
        .Setup(m => 
            m.GetFile(
                It.IsAny<IFileConnection>(), 
                It.IsAny<string>(), 
                It.IsAny<string>()
            ))
        .Throws<System.IO.IOException>();

    methodTester.Object.TransferFiles("foo1", "foo2");
    Assert.IsTrue(methodTester.Object.Status == TransferStatus.TransferInterrupted);
}

If there is a problem with this method, I would like to know; the other answers suggest I am doing this wrong, but this was exactly what I was trying to do.