How can I test a custom DelegatingHandler in the ASP.NET MVC 4 Web API?

Question

I\'ve seen this question come up in a few places, and not seen any great answers. As I\'ve had to do this myself a few times, I thought I\'d post my solution. If you have an

Answer 1

I created the following for testing DelegatingHandlers. It is useful for handlers that use the HttpRequestMessage.DependencyScope to resolve dependencies using your favorite IoC framework e.g. a WindsorDependencyResolver with a WindsorContainer:

    public class UnitTestHttpMessageInvoker : HttpMessageInvoker
    {
        private readonly HttpConfiguration configuration;

        public UnitTestHttpMessageInvoker(HttpMessageHandler handler, IDependencyResolver resolver)
        : base(handler, true)
        {
            this.configuration = new HttpConfiguration();
            configuration.DependencyResolver = resolver;
        }

        [DebuggerNonUserCode]
        public override Task SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            if (request == null)
            {
                throw new ArgumentNullException("request");
            }

            request.Properties["MS_HttpConfiguration"] = this.configuration;
            return base.SendAsync(request, cancellationToken);
        }
    }