[MVC.Testing] Fix NullReferenceException

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

@@ -103,7 +103,7 @@ public virtual IServiceProvider Services
             StartServer();
             if (_useKestrel)
             {
-                return _webHost!.Services;
+                return _webHost?.Services ?? _host!.Services;
             }
 
             return _host?.Services ?? _server!.Host.Services;
@@ -263,8 +263,8 @@ public void StartServer()
         {
             var deferredHostBuilder = new DeferredHostBuilder();
             deferredHostBuilder.UseEnvironment(Environments.Development);
-            // There's no helper for UseApplicationName, but we need to 
-            // set the application name to the target entry point 
+            // There's no helper for UseApplicationName, but we need to
+            // set the application name to the target entry point
             // assembly name.
             deferredHostBuilder.ConfigureHostConfiguration(config =>
             {

src/Mvc/test/Mvc.FunctionalTests/KestrelBasedWebApplicationFactoryForMinimal.cs

@@ -0,0 +1,15 @@
+// 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 KestrelBasedWebApplicationFactoryForMinimal : WebApplicationFactory<SimpleWebSiteWithWebApplicationBuilder.Program>
+{
+    public KestrelBasedWebApplicationFactoryForMinimal() : base()
+    {
+        // Use dynamically assigned port to avoid test conflicts in CI.
+        this.UseKestrel(0);
+    }
+}

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

@@ -4,6 +4,8 @@
 using System.Net;
 using System.Net.Http;
 using System.Net.Http.Headers;
+using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.AspNetCore.Mvc.FunctionalTests;
 
@@ -40,9 +42,6 @@ public async Task RetrievesDataFromRealServer()
     [Fact]
     public async Task ServerReachableViaGenericHttpClient()
     {
-        // Arrange
-        var baseAddress = new Uri("http://localhost:5000");
-
         // Act
         using var factoryClient = Factory.CreateClient();
         using var client = new HttpClient() { BaseAddress = factoryClient.BaseAddress };
@@ -52,4 +51,15 @@ public async Task ServerReachableViaGenericHttpClient()
         // Assert
         Assert.Equal(HttpStatusCode.OK, response.StatusCode);
     }
+
+    [Fact]
+    public void CanResolveServices()
+    {
+        // Act
+        var server = Factory.Services.GetRequiredService<IServer>();
+
+        // Assert
+        Assert.NotNull(server);
+        Assert.Contains("Kestrel", server.GetType().FullName);
+    }
 }

src/Mvc/test/Mvc.FunctionalTests/RealServerUsingMinimalBackedIntegrationTests.cs

@@ -0,0 +1,62 @@
+// 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;
+using System.Net.Http.Headers;
+using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.AspNetCore.Mvc.FunctionalTests;
+
+public class RealServerUsingMinimalBackedIntegrationTests : IClassFixture<KestrelBasedWebApplicationFactoryForMinimal>
+{
+    public KestrelBasedWebApplicationFactoryForMinimal Factory { get; }
+
+    public RealServerUsingMinimalBackedIntegrationTests(KestrelBasedWebApplicationFactoryForMinimal factory)
+    {
+        Factory = factory;
+    }
+
+    [Fact]
+    public async Task RetrievesDataFromRealServer()
+    {
+        // Arrange
+        var expectedMediaType = MediaTypeHeaderValue.Parse("text/plain; 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.Contains("Hello World", responseContent);
+    }
+
+    [Fact]
+    public async Task ServerReachableViaGenericHttpClient()
+    {
+        // Act
+        using var factoryClient = Factory.CreateClient();
+        using var client = new HttpClient() { BaseAddress = factoryClient.BaseAddress };
+
+        using var response = await client.GetAsync("/");
+
+        // Assert
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+    }
+
+    [Fact]
+    public void CanResolveServices()
+    {
+        // Act
+        var server = Factory.Services.GetRequiredService<IServer>();
+
+        // Assert
+        Assert.NotNull(server);
+        Assert.Contains("Kestrel", server.GetType().FullName);
+    }
+}

src/Mvc/test/Mvc.FunctionalTests/RealServerWithDynamicPortIntegrationTests.cs

@@ -3,7 +3,6 @@
 
 using System.Net;
 using System.Net.Http;
-using System.Net.Http.Headers;
 using Microsoft.AspNetCore.Mvc.Testing;
 
 namespace Microsoft.AspNetCore.Mvc.FunctionalTests;