Add test for link generation with high priority required parameter (#869)

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

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Routing.TestObjects;
 using Microsoft.Extensions.DependencyInjection;
 using Xunit;
@@ -597,6 +598,64 @@ namespace Microsoft.AspNetCore.Routing
             Assert.NotSame(original, actual);
         }
 
+        [Fact]
+        public void GetPathByRouteValues_UsesFirstTemplateThatSucceeds()
+        {
+            // Arrange
+            var endpointControllerAction = EndpointFactory.CreateRouteEndpoint(
+                "Home/Index",
+                order: 3,
+                defaults: new { controller = "Home", action = "Index", },
+                metadata: new[] { new RouteValuesAddressMetadata(new RouteValueDictionary(new { controller = "Home", action = "Index", })) });
+            var endpointController = EndpointFactory.CreateRouteEndpoint(
+                "Home",
+                order: 2,
+                defaults: new { controller = "Home", action = "Index", },
+                metadata: new[] { new RouteValuesAddressMetadata(new RouteValueDictionary(new { controller = "Home", action = "Index", })) });
+            var endpointEmpty = EndpointFactory.CreateRouteEndpoint(
+                "",
+                order: 1,
+                defaults: new { controller = "Home", action = "Index", },
+                metadata: new[] { new RouteValuesAddressMetadata(new RouteValueDictionary(new { controller = "Home", action = "Index", })) });
+
+            // This endpoint should be used to generate the link when an id is present
+            var endpointControllerActionParameter = EndpointFactory.CreateRouteEndpoint(
+                "Home/Index/{id}",
+                order: 0,
+                defaults: new { controller = "Home", action = "Index", },
+                metadata: new[] { new RouteValuesAddressMetadata(new RouteValueDictionary(new { controller = "Home", action = "Index", })) });
+
+            var linkGenerator = CreateLinkGenerator(endpointControllerAction, endpointController, endpointEmpty, endpointControllerActionParameter);
+
+            var context = new EndpointSelectorContext()
+            {
+                RouteValues = new RouteValueDictionary(new { controller = "Home", action = "Index", })
+            };
+            var httpContext = CreateHttpContext();
+            httpContext.Features.Set<IRouteValuesFeature>(context);
+
+            // Act
+            var pathWithoutId = linkGenerator.GetPathByRouteValues(
+                httpContext,
+                routeName: null,
+                values: new RouteValueDictionary());
+
+            var pathWithId = linkGenerator.GetPathByRouteValues(
+                httpContext,
+                routeName: null,
+                values: new RouteValueDictionary(new { id = "3" }));
+
+            var pathWithCustom = linkGenerator.GetPathByRouteValues(
+                httpContext,
+                routeName: null,
+                values: new RouteValueDictionary(new { custom = "Custom" }));
+
+            // Assert
+            Assert.Equal("/", pathWithoutId);
+            Assert.Equal("/Home/Index/3", pathWithId);
+            Assert.Equal("/?custom=Custom", pathWithCustom);
+        }
+
         protected override void AddAdditionalServices(IServiceCollection services)
         {
             services.AddSingleton<IEndpointAddressScheme<int>, IntAddressScheme>();