Add new constructor to TestSever which allows providing preconfigured FeatureCollection to use before Build / Start is invoked. (#967)

src/Microsoft.AspNetCore.TestHost/TestServer.cs

@@ -21,7 +21,23 @@ namespace Microsoft.AspNetCore.TestHost
         private IHttpApplication<Context> _application;
 
         public TestServer(IWebHostBuilder builder)
+            : this(builder, new FeatureCollection())
         {
+        }
+
+        public TestServer(IWebHostBuilder builder, IFeatureCollection featureCollection)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+            if (featureCollection == null)
+            {
+                throw new ArgumentNullException(nameof(featureCollection));
+            }        
+        
+            Features = featureCollection;
+
             var host = builder.UseServer(this).Build();
             host.Start();
             _hostInstance = host;
@@ -37,7 +53,7 @@ namespace Microsoft.AspNetCore.TestHost
             }
         }
 
-        IFeatureCollection IServer.Features { get; }
+        public IFeatureCollection Features { get; }
 
         public HttpMessageHandler CreateHandler()
         {

test/Microsoft.AspNetCore.TestHost.Tests/TestServerTests.cs

@@ -9,6 +9,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Hosting.Server.Features;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Testing.xunit;
@@ -119,6 +120,39 @@ namespace Microsoft.AspNetCore.TestHost
             Assert.Equal("ApplicationServicesEqual:True", result);
         }
 
+        [Fact]
+        public void TestServerConstructorWithFeatureCollectionAllowsInitializingServerFeatures()
+        {
+            // Arrange
+            var url = "http://localhost:8000/appName/serviceName";
+            var builder = new WebHostBuilder()
+                .UseUrls(url)
+                .Configure(applicationBuilder =>
+                {
+                    var serverAddressesFeature = applicationBuilder.ServerFeatures.Get<IServerAddressesFeature>();
+                    Assert.Contains(serverAddressesFeature.Addresses, s => string.Equals(s, url, StringComparison.Ordinal));
+                });
+
+
+            var featureCollection = new FeatureCollection();
+            featureCollection.Set<IServerAddressesFeature>(new ServerAddressesFeature());
+
+            // Act
+            new TestServer(builder, featureCollection);
+
+            // Assert
+            // Is inside configure callback
+        }
+
+        [Fact]
+        public void TestServerConstructorWithNullFeatureCollectionThrows()
+        {
+            var builder = new WebHostBuilder()
+                .Configure(b => { });
+
+            Assert.Throws<ArgumentNullException>(() => new TestServer(builder, null));
+        }
+
         public class TestService { }
 
         public class TestRequestServiceMiddleware