Integration Testing - How to hit endpoints using Microsoft.Owin.Testing.TestServer?

Question

I have setup a basic Web API project to test writing integration tests, with the below setup

Startup:

using Microsoft.Owin;
using Owin;

[assembly: OwinStartup(typeof(WebApiTest.Startup))]

namespace WebApiTest
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            WebApiConfig.Register(new System.Web.Http.HttpConfiguration());
        }
    }
}

And the following controller:

using System.Web.Http;

namespace WebApiTest.Controllers
{
    public class TestController : ApiController
    {
        public IHttpActionResult Post()
        {
            return Ok("Hello, world!");
        }
    }
}

For my Tests project I am using NUnit for my testing, and have two classes: an abstract BaseTest class, and a ControllerTests class which contains one test with the intention of sending a web request out to the above TestController's GET Action method:

BaseTest:

using Microsoft.Owin.Testing;
using NUnit.Framework;
using System;
using System.Net.Http;

namespace WebApiTest.Tests
{
    public abstract class BaseTest : IDisposable
    {
        protected const string _url = "http://localhost/";
        protected TestServer _server;

        public void Dispose()
        {
            _server.Dispose();
        }

        [SetUp]
        public void SetUp()
        {
            _server = TestServer.Create<Startup>();
        }

        protected HttpRequestMessage CreateRequest(string url, string 
contentType, HttpMethod method)
        {
            HttpRequestMessage request = new HttpRequestMessage
            {
                RequestUri = new Uri(_url + url),
                Method = method
            };
            request.Headers.Accept.Add(new 
System.Net.Http.Headers.MediaTypeWithQualityHeaderValue(contentType));
            return request;
        }
    }
}

ControllerTests:

using FluentAssertions;
using NUnit.Framework;
using System.Net;
using System.Net.Http;
using System.Threading.Tasks;

namespace WebApiTest.Tests
{
    [TestFixture]
    public class ControllerTests : BaseTest
    {
        [Test]
        public async Task Test1()
        {
            HttpRequestMessage request = CreateRequest("test", "application/json", HttpMethod.Post);
            HttpResponseMessage response = await _server.HttpClient.SendAsync(request);
            response.StatusCode.Should().Be(HttpStatusCode.OK);
        }
    }
}

The problem I am running into is that I'm not able to reach my endpoint with the call await _server.HttpClient.SendAsync(request); as I always get a 404: Not Found response.

I'm not entirely sure what I'm doing wrong, whether it be something that's not being setup property or Api routes that aren't being mapped.

update: Here is my WebApiConfig.Register() method for reference:

public static void Register(HttpConfiguration config)
{
    config.MapHttpAttributeRoutes();
    config.Routes.MapHttpRoute(
        name: "DefaultApi",
        routeTemplate: "api/{controller}/{id}",
        defaults: new { id = RouteParameter.Optional }
    );
}

Answer 1

The web API was not configured correctly so the routes are not known to it

If you are self-hosting with OWIN, create a new HttpConfiguration instance. Perform any configuration on this instance, and then pass the instance to the Owin.UseWebApi extension method.

public class Startup {
    public void Configuration(IAppBuilder app) {
        var config = new System.Web.Http.HttpConfiguration();
        WebApiConfig.Register(config);
        app.UseWebApi(config); //<-- THIS WAS MISSING 
    }
}

Reference Configuring Web API with OWIN Self-Hosting