Throwing an exception nulls any out parameters

[JefWight]

I'm trying to abstract making web requests. I've written an interface to replace both the Request and Response portions. To enable the most complete support for mocking, the design is such that void GetResponse(out IResponse response); is expected to set the response value even on WebException (if the exception has a Response property that's an HttpWebResponse). This allows me to to use the interface to extract info about the response even in a WebException.

In my test code, I've tried:

ISetup<IRequestMessage<IResponseMessage>> getResponse = request.Setup(r => r.GetResponse(out response));
getResponse.Throws(exceptionToThrow);

I've also tried approximately what I found on stack overflow by attempting to set a "callback" that would explicitly set the out parameter then throw:

public delegate void OutAction(out IResponseMessage response);
private static void SetOutThenThrow(this ICallback mock, IResponseMessage response, Exception exceptionToThrow)
{
    OutAction foo = (out IResponseMessage r) =>
        {
            r = response;
            throw exceptionToThrow;
        };

    mock.GetType()
        .Assembly.GetType("Moq.MethodCall")
        .InvokeMember("SetCallbackWithArguments", BindingFlags.InvokeMethod | BindingFlags.NonPublic | BindingFlags.Instance, null, mock, new[] { foo });
}

While both approaches throw an exception as expected, neither of these approaches result in the out parameter being set in the calling code.

I suspect this has something to do with the way the reflection code is executing.

[stakx]

Hi @JefWight, thanks for the report. Could you please post a brief but complete code example that reproduces this issue? (Please try to avoid doing reflection over Moq internals in the repro code. Try to show what you're attempting to do using the public API.) Thanks!

[JeffyW]

Sorry, it looks like this was just a bug in the version our test tools was using (4.0.10827), but when I create a test project and use the latest version, it works correctly. For reference, here's the code that doesn't work in 4.0.10827:

namespace UnitTest
{
    using System;
    using Microsoft.VisualStudio.TestTools.UnitTesting;
    using Moq;

    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public void TestOutParameterWorksWithThrows()
        {
            var mockTest = new Mock<ITest>();
            var test = mockTest.Object;

            var outString = "test";
            var tryDoSomething = mockTest.Setup(t => t.TryDoSomething(out outString));

            string newOutString = null;
            tryDoSomething.Throws<TimeoutException>();
            try
            {
                var result = test.TryDoSomething(out newOutString);
            }
            catch (TimeoutException)
            {
            }

            Assert.AreEqual(outString, newOutString);
        }

        public interface ITest
        {
            bool TryDoSomething(out string value);
        }
    }
}

Feel free to close this out.

[stakx]

Thanks for replying. Since we're not fixing old versions :) I'll close this.