Add some tests, rename misnamed file

src/Microsoft.AspNetCore.Routing/RoutingBuilderExtensions.cs

@@ -61,6 +61,14 @@ namespace Microsoft.AspNetCore.Builder
                 throw new ArgumentNullException(nameof(action));
             }
 
+            if (builder.ApplicationServices.GetService(typeof(RoutingMarkerService)) == null)
+            {
+                throw new InvalidOperationException(Resources.FormatUnableToFindServices(
+                    nameof(IServiceCollection),
+                    nameof(RoutingServiceCollectionExtensions.AddRouting),
+                    "ConfigureServices(...)"));
+            }
+
             var routeBuilder = new RouteBuilder(builder);
             action(routeBuilder);
 

test/Microsoft.AspNetCore.Routing.Tests/RoutingBuilderExtensionsTest.cs

@@ -0,0 +1,116 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder.Internal;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.AspNetCore.Routing.Internal;
+using Microsoft.Extensions.DependencyInjection;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    public class RoutingBuilderExtensionsTest
+    {
+        [Fact]
+        public void UseRouter_IRouter_ThrowsWithoutCallingAddRouting()
+        {
+            // Arrange
+            var app = new ApplicationBuilder(Mock.Of<IServiceProvider>());
+
+            // Act
+            var ex = Assert.Throws<InvalidOperationException>(() => app.UseRouter(Mock.Of<IRouter>()));
+
+            // Assert
+            Assert.Equal(
+                "Unable to find the required services. " +
+                "Please add all the required services by calling 'IServiceCollection.AddRouting' " +
+                "inside the call to 'ConfigureServices(...)' in the application startup code.",
+                ex.Message);
+        }
+
+        [Fact]
+        public void UseRouter_Action_ThrowsWithoutCallingAddRouting()
+        {
+            // Arrange
+            var app = new ApplicationBuilder(Mock.Of<IServiceProvider>());
+
+            // Act
+            var ex = Assert.Throws<InvalidOperationException>(() => app.UseRouter(b => { }));
+
+            // Assert
+            Assert.Equal(
+                "Unable to find the required services. " +
+                "Please add all the required services by calling 'IServiceCollection.AddRouting' " +
+                "inside the call to 'ConfigureServices(...)' in the application startup code.",
+                ex.Message);
+        }
+
+        [Fact]
+        public async Task UseRouter_IRouter_CallsRoute()
+        {
+            // Arrange
+            var services = CreateServices();
+
+            var app = new ApplicationBuilder(services);
+
+            var router = new Mock<IRouter>(MockBehavior.Strict);
+            router
+                .Setup(r => r.RouteAsync(It.IsAny<RouteContext>()))
+                .Returns(TaskCache.CompletedTask)
+                .Verifiable();
+
+            app.UseRouter(router.Object);
+
+            var appFunc = app.Build();
+
+            // Act
+            await appFunc(new DefaultHttpContext());
+
+            // Assert
+            router.Verify();
+        }
+
+        [Fact]
+        public async Task UseRouter_Action_CallsRoute()
+        {
+            // Arrange
+            var services = CreateServices();
+
+            var app = new ApplicationBuilder(services);
+
+            var router = new Mock<IRouter>(MockBehavior.Strict);
+            router
+                .Setup(r => r.RouteAsync(It.IsAny<RouteContext>()))
+                .Returns(TaskCache.CompletedTask)
+                .Verifiable();
+
+            app.UseRouter(b =>
+            {
+                b.Routes.Add(router.Object);
+            });
+
+            var appFunc = app.Build();
+
+            // Act
+            await appFunc(new DefaultHttpContext());
+
+            // Assert
+            router.Verify();
+        }
+
+        private IServiceProvider CreateServices()
+        {
+            var services = new ServiceCollection();
+
+            services.AddLogging();
+            services.AddOptions();
+            services.AddRouting();
+
+            return services.BuildServiceProvider();
+        }
+    }
+}