How can I create a WebException with an FtpWebResponse for testing?

Question

I'm using FtpWebRequest and a Transient Fault Handling application block. For my fault handler, I have an error detection strategy that checks if the response is considered transient so that it knows whether or not to retry:

public bool IsTransient(Exception ex)
    {

        var isTransient = false;
        //will be false if the exception is not a web exception.
        var webEx = ex as WebException;

        //happens when receiving a protocol error.
        //This protocol error wraps the inner exception, e.g. a 401 access denied.
        if (webEx != null && webEx.Status == WebExceptionStatus.ProtocolError)
        {
            var response = webEx.Response as FtpWebResponse;
            if (response != null && (int)response.StatusCode < 400)
            {
                isTransient = true;
            }
        }
        // if it is a web exception but not a protocol error,
        // check the status code.
        else if (webEx != null)
        {
            //(check for transient error statuses here...)
            isTransient = true;
        }

        return isTransient;
    }

I'm trying to write some tests to check that things the appropriate errors are flagged as transient, but I'm having trouble creating or mocking a web exception that has an inner exception with an FtpWebResponse (so that the response in the following isn't always null)

var response = webEx.Response as FtpWebResponse;

Does anybody know how I can do this? Am I going about it the right way?

Answer 1

Use the appropriate constructor on WebException to set the response:

public WebException(
 string message,
 Exception innerException,
 WebExceptionStatus status,
 WebResponse response)

---

setting up an exception with an FtpWebResponse is the bit that I'm having trouble with... FtpWebResponse has an internal constructor that I can't access.

The BCL is not really made for testing because that concept wasn't big at the time it was written. You'll have to call that internal constructor using reflection (use a decompiler to see what's available). Or, wrap all of the System.Net classes that you need with custom mockable classes. That looks like a lot of work, though.

Answer 2

I build my off line tests using an stub of FtpWebResponse, created by Rhino Framework

Example:

public WebException createExceptionHelper(String message, WebExceptionStatus webExceptionStatus, FtpStatusCode serverError )
{
    var ftpWebResponse = Rhino.Mocks.MockRepository.GenerateStub<FtpWebResponse>();
    ftpWebResponse.Stub(f => f.StatusCode).Return(serverError);
    ftpWebResponse.Stub(f => f.ResponseUri).Return(new Uri("http://mock.localhost"));

    //now just pass the ftpWebResponse stub object to the constructor
    return new WebException(message, null, webExceptionStatus, ftpWebResponse);
    }