UrlHelperFactory.GetUrlHelper may throw an exception

[vdachev]

While trying to mock a controller I came across a KeyNotFoundException in the UrlHelperFactory's GetUrlHelper method.

It seems the following code relies on the typeof(IUrlHelper) key already populated in the Items collection:

// Perf: Create only one UrlHelper per context
var urlHelper = httpContext.Items[typeof(IUrlHelper)] as IUrlHelper;
if (urlHelper == null)
{
   urlHelper = new UrlHelper(context);
   httpContext.Items[typeof(IUrlHelper)] = urlHelper;
}

If the key is missing, this line throws an exception, instead of returning null. I believe that the following code should be used instead:

// Perf: Create only one UrlHelper per context
object urlHelper;
if (!httpContext.Items.TryGetvalue(typeof(IUrlHelper), out urlHelper)
    || !(urlHelper is IUrlHelper))
{
    urlHelper = new UrlHelper(context);
    httpContext.Items[typeof(IUrlHelper)] = urlHelper;
}

return (IUrlHelper)urlHelper;

[rynowak]

Did you create a mock for HttpContext.Items? Right now this code expects Items to return null on a missing key, which is something we should probably fix since it's specified as IDictionary<>.

Regardless, I'd strongly suggest using DefaultHttpContext in your tests - you'll need less mock setup stuff. It's what we do and we haven't run into any limitations.