Added a test utilizing UseKestrel option of WebApplicationFactory.

Author: mkArtakMSFT

src/Mvc/Mvc.Testing/src/WebApplicationFactory.cs

@@ -31,6 +31,7 @@ public partial class WebApplicationFactory<TEntryPoint> : IDisposable, IAsyncDis
     private IHost? _host;
     private Action<IWebHostBuilder> _configuration;
     private IWebHost? _webHost;
+    private Uri _webHostAddress;
     private readonly List<HttpClient> _clients = new();
     private readonly List<WebApplicationFactory<TEntryPoint>> _derivedFactories = new();
 
@@ -221,6 +222,14 @@ private void EnsureServer()
             if (_useKestrel)
             {
                 _webHost = CreateKestrelServer(builder);
+
+                var serverAddressFeature = _webHost.ServerFeatures.Get<IServerAddressesFeature>();
+                if (serverAddressFeature?.Addresses.Count > 0)
+                {
+                    // Store the web host address as it's going to be used every time a client is created to communicate to the server
+                    _webHostAddress = new Uri(serverAddressFeature.Addresses.Last());
+                    ClientOptions.BaseAddress = _webHostAddress;
+                }
             }
             else
             {
@@ -492,8 +501,19 @@ protected virtual void ConfigureWebHost(IWebHostBuilder builder)
     /// redirects and handles cookies.
     /// </summary>
     /// <returns>The <see cref="HttpClient"/>.</returns>
-    public HttpClient CreateClient() =>
-        CreateClient(ClientOptions);
+    public HttpClient CreateClient()
+    {
+        var client = CreateClient(ClientOptions);
+
+        if (_useKestrel)
+        {
+            // Have to do this, as the ClientOptions.BaseAddress will be set to poitn to the kestrel server,
+            // and it may not match the original base address value.
+            client.BaseAddress = ClientOptions.BaseAddress;
+        }
+
+        return client;
+    }
 
     /// <summary>
     /// Creates an instance of <see cref="HttpClient"/> that automatically follows
@@ -586,12 +606,7 @@ protected virtual void ConfigureClient(HttpClient client)
                 throw new InvalidOperationException(Resources.ServerNotInitialized);
             }
 
-            // The server should be started at this point already.
-            var serverAddressFeature = _webHost.ServerFeatures.Get<IServerAddressesFeature>();
-            if (serverAddressFeature?.Addresses.Count > 0)
-            {
-                client.BaseAddress = new Uri(serverAddressFeature.Addresses.Last());
-            }
+            client.BaseAddress = _webHostAddress;
         }
         else
         {

src/Mvc/test/Mvc.FunctionalTests/KestrelBasedWapFactory.cs

@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Mvc.Testing;
+
+namespace Microsoft.AspNetCore.Mvc.FunctionalTests;
+
+public class KestrelBasedWapFactory : WebApplicationFactory<SimpleWebSite.Startup>
+{
+    public KestrelBasedWapFactory() : base()
+    {
+        this.UseKestrel();
+    }
+}

src/Mvc/test/Mvc.FunctionalTests/RealServerBackedIntegrationTests.cs

@@ -0,0 +1,40 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Net;
+using System.Net.Http.Headers;
+
+namespace Microsoft.AspNetCore.Mvc.FunctionalTests;
+
+public class RealServerBackedIntegrationTests : IClassFixture<KestrelBasedWapFactory>
+{
+    public KestrelBasedWapFactory Factory { get; }
+
+    public RealServerBackedIntegrationTests(KestrelBasedWapFactory factory)
+    {
+        Factory = factory;
+    }
+
+    [Fact]
+    public async Task RetrievesDataFromRealServer()
+    {
+        // Arrange
+        var expectedMediaType = MediaTypeHeaderValue.Parse("application/json; charset=utf-8");
+
+        // Act
+        var client = Factory.CreateClient();
+        var response = await client.GetAsync("/");
+        var responseContent = await response.Content.ReadAsStringAsync();
+
+        // Assert
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        Assert.Equal(expectedMediaType, response.Content.Headers.ContentType);
+
+        Assert.Equal(5000, client.BaseAddress.Port);
+
+        Assert.Contains("first", responseContent);
+        Assert.Contains("second", responseContent);
+        Assert.Contains("wall", responseContent);
+        Assert.Contains("floor", responseContent);
+    }
+}