Nunit async test exception assertion

Question

[Edit (May 2020)] - This issue has been reportedly addressed in newer releases of NUnit. Please see Nunit.ThrowsAsync. (Ref this answer, thanks @James-Ross)

Answer 1

This blog talks about problems similar to mine.

I followed the recommendation proposed there, and have a test like this -

    [Test]
    public void ShouldThrow404WhenNotFound()
    {
        var mockUserRepository = new Mock();
        mockUserRepository.Setup(x => x.GetByUserName(It.IsAny())).Returns(default(User));
        var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() };

        var aggregateException = Assert.Throws(() => userController.Get("foo").Wait());
        var httpResponseException = aggregateException.InnerExceptions
            .FirstOrDefault(x => x.GetType() == typeof(HttpResponseException)) as HttpResponseException;

        Assert.That(httpResponseException, Is.Not.Null);
        Assert.That(httpResponseException.Response.StatusCode, Is.EqualTo(HttpStatusCode.NotFound));
    }

I am not too pleased with it, but this works.

EDIT 1

Inspired by @StephenCleary, I added a static helper class that does the asserts that I am looking for. It looks like this -

public static class AssertEx
{
    public static async Task ThrowsAsync(Func func) where TException : class
    {
        await ThrowsAsync(func, exception => { });
    } 

    public static async Task ThrowsAsync(Func func, Action action) where TException : class
    {
        var exception = default(TException);
        var expected = typeof(TException);
        Type actual = null;
        try
        {
            await func();
        }
        catch (Exception e)
        {
            exception = e as TException;
            actual = e.GetType();
        }

        Assert.AreEqual(expected, actual);
        action(exception);
    }
}

I can now have a test like -

    [Test]
    public async void ShouldThrow404WhenNotFound()
    {
        var mockUserRepository = new Mock();
        mockUserRepository.Setup(x => x.GetByUserName(It.IsAny())).Returns(default(User));
        var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() };

        Action asserts = exception => Assert.That(exception.Response.StatusCode, Is.EqualTo(HttpStatusCode.NotFound));
        await AssertEx.ThrowsAsync(() => userController.Get("foo"), asserts);
    }