Fixed the errors and test failures.

Author: mkArtakMSFT

src/Mvc/Mvc.Testing/src/PublicAPI.Shipped.txt

@@ -16,7 +16,6 @@ Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.CreateDefaul
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.CreateDefaultClient(System.Uri! baseAddress, params System.Net.Http.DelegatingHandler![]! handlers) -> System.Net.Http.HttpClient!
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.Dispose() -> void
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.Factories.get -> System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint!>!>!
-Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.Server.get -> Microsoft.AspNetCore.TestHost.TestServer!
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.WebApplicationFactory() -> void
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.WithWebHostBuilder(System.Action<Microsoft.AspNetCore.Hosting.IWebHostBuilder!>! configuration) -> Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint!>!
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactoryClientOptions
@@ -41,7 +40,6 @@ virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.Conf
 virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.ConfigureWebHost(Microsoft.AspNetCore.Hosting.IWebHostBuilder! builder) -> void
 virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.CreateHost(Microsoft.Extensions.Hosting.IHostBuilder! builder) -> Microsoft.Extensions.Hosting.IHost!
 virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.CreateHostBuilder() -> Microsoft.Extensions.Hosting.IHostBuilder?
-virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.CreateServer(Microsoft.AspNetCore.Hosting.IWebHostBuilder! builder) -> Microsoft.AspNetCore.TestHost.TestServer!
 virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.CreateWebHostBuilder() -> Microsoft.AspNetCore.Hosting.IWebHostBuilder?
 virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.Dispose(bool disposing) -> void
 virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.DisposeAsync() -> System.Threading.Tasks.ValueTask

src/Mvc/Mvc.Testing/src/PublicAPI.Unshipped.txt

@@ -2,3 +2,4 @@
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.Initialize() -> void
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.Server.get -> Microsoft.AspNetCore.TestHost.TestServer?
 Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.TestServer.get -> Microsoft.AspNetCore.TestHost.ITestServer?
+virtual Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory<TEntryPoint>.CreateServer(Microsoft.AspNetCore.Hosting.IWebHostBuilder! builder) -> Microsoft.AspNetCore.TestHost.ITestServer!

src/Mvc/Mvc.Testing/src/Resources.resx

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <root>
   <!-- 
     Microsoft ResX Schema 
@@ -120,6 +120,9 @@
   <data name="InvalidAssemblyEntryPoint" xml:space="preserve">
     <value>The provided Type '{0}' does not belong to an assembly with an entry point. A common cause for this error is providing a Type from a class library.</value>
   </data>
+  <data name="InvalidTestServerConfiguration" xml:space="preserve">
+    <value>The host doesn't contain a valid ITestServer configuration.</value>
+  </data>
   <data name="MissingBuilderMethod" xml:space="preserve">
     <value>No method 'public static {0} CreateHostBuilder(string[] args)' or 'public static {1} CreateWebHostBuilder(string[] args)' found on '{2}'. Alternatively, {3} can be extended and '{4}' or '{5}' can be overridden to provide your own instance.</value>
   </data>

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

@@ -37,7 +37,6 @@ public partial class WebApplicationFactory<TEntryPoint> : IDisposable, IAsyncDis
     private readonly List<HttpClient> _clients = new();
     private readonly List<WebApplicationFactory<TEntryPoint>> _derivedFactories = new();
 
-
     /// <summary>
     /// <para>
     /// Creates an instance of <see cref="WebApplicationFactory{TEntryPoint}"/>. This factory can be used to
@@ -94,7 +93,7 @@ public ITestServer? TestServer
         get
         {
             Initialize();
-            return _server!;
+            return _server;
         }
     }
 
@@ -157,7 +156,8 @@ internal virtual WebApplicationFactory<TEntryPoint> WithWebHostBuilderCore(Actio
     /// <summary>
     /// Initializes the instance by configurating the host builder.
     /// </summary>
-    /// <exception cref="InvalidOperationException">Thrown if the provided <see cref="TEntryPoint"/> type has no factory method.</exception>
+    /// <exception cref="InvalidOperationException">Thrown if the provided <typeparamref name="TEntryPoint"/> type has no factory method.</exception>
+    [MemberNotNull(nameof(_server))]
     public void Initialize()
     {
         if (_server != null)
@@ -233,6 +233,10 @@ private void ConfigureHostBuilder(IHostBuilder hostBuilder)
         });
         _host = CreateHost(hostBuilder);
         _server = _host.Services.GetRequiredService<IServer>() as ITestServer;
+        if (_server is null)
+        {
+            throw new InvalidOperationException(Resources.InvalidTestServerConfiguration);
+        }
     }
 
     private void SetContentRoot(IWebHostBuilder builder)

src/Mvc/test/Mvc.FunctionalTests/ApiExplorerTest.cs

@@ -1573,7 +1573,7 @@ public async Task ApiExplorer_LogsInvokedDescriptionProvidersOnStartup()
     [Fact]
     public void ApiExplorer_BuildsMetadataForActionWithTypedResult()
     {
-        var apiDescCollectionProvider = Factory.Server.Services.GetService<IApiDescriptionGroupCollectionProvider>();
+        var apiDescCollectionProvider = Factory.Services.GetService<IApiDescriptionGroupCollectionProvider>();
         var testGroupName = nameof(ApiExplorerWithTypedResultController).Replace("Controller", string.Empty);
         var group = apiDescCollectionProvider.ApiDescriptionGroups.Items.Where(i => i.GroupName == testGroupName).SingleOrDefault();
         Assert.NotNull(group);

src/Mvc/test/Mvc.FunctionalTests/ComponentRenderingFunctionalTests.cs

@@ -198,7 +198,7 @@ private HttpClient CreateClient(
 
         // We configure the inner handler with a handler to this TestServer instance so that calls to the
         // server can get routed properly.
-        loopHandler.InnerHandler = fixture.Server.CreateHandler();
+        loopHandler.InnerHandler = fixture.TestServer.CreateHandler();
 
         void ConfigureTestWeatherForecastService(IServiceCollection services) =>
             // We configure the test service here with an HttpClient that uses this loopback handler to talk

src/Mvc/test/Mvc.FunctionalTests/Infrastructure/MvcTestFixture.cs

@@ -42,7 +42,7 @@ protected override void ConfigureWebHost(IWebHostBuilder builder)
                 });
     }
 
-    protected override TestServer CreateServer(IWebHostBuilder builder)
+    protected override ITestServer CreateServer(IWebHostBuilder builder)
     {
         var originalCulture = CultureInfo.CurrentCulture;
         var originalUICulture = CultureInfo.CurrentUICulture;

src/Mvc/test/Mvc.FunctionalTests/TestingInfrastructureInheritanceTests.cs

@@ -141,7 +141,7 @@ protected override void ConfigureWebHost(IWebHostBuilder builder)
             base.ConfigureWebHost(builder);
         }
 
-        protected override TestServer CreateServer(IWebHostBuilder builder)
+        protected override ITestServer CreateServer(IWebHostBuilder builder)
         {
             CreateServerCalled = true;
             return base.CreateServer(builder);