add test for FallbackToHttpMessageHandler

Author: dameng324

test/Microsoft.NET.Build.Containers.UnitTests/FallbackToHttpMessageHandlerTests.cs

@@ -0,0 +1,71 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace Microsoft.NET.Build.Containers.UnitTests
+{
+    public class FallbackToHttpMessageHandlerTests
+    {
+        [Theory]
+        [InlineData("mcr.microsoft.com", 80)]
+        [InlineData("mcr.microsoft.com:443", 443)]
+        [InlineData("mcr.microsoft.com:80", 80)]
+        [InlineData("mcr.microsoft.com:5555", 5555)]
+        public async Task FallBackToHttpPortShouldAsExpected(string registry, int expectedPort)
+        {
+            var uri = new UriBuilder($"https://{registry}").Uri;
+            var handler = new FallbackToHttpMessageHandler(
+                registry,
+                uri.Host,
+                uri.Port,
+                new ServerMessageHandler(request =>
+                {
+                    // only accept http requests, reject https requests with a secure connection error
+
+                    if (request.RequestUri!.Scheme == Uri.UriSchemeHttps)
+                    {
+                        throw new HttpRequestException(
+                            httpRequestError: HttpRequestError.SecureConnectionError
+                        );
+                    }
+                    else
+                    {
+                        return new HttpResponseMessage(HttpStatusCode.OK)
+                        {
+                            RequestMessage = request,
+                        };
+                    }
+                }),
+                NullLogger.Instance
+            );
+            using var httpClient = new HttpClient(handler);
+            var response = await httpClient.GetAsync(uri);
+            Assert.Equal(expectedPort, response.RequestMessage?.RequestUri?.Port);
+        }
+
+        private sealed class ServerMessageHandler : HttpMessageHandler
+        {
+            private readonly Func<HttpRequestMessage, HttpResponseMessage> _server;
+
+            public ServerMessageHandler(Func<HttpRequestMessage, HttpResponseMessage> server)
+            {
+                _server = server;
+            }
+
+            protected override Task<HttpResponseMessage> SendAsync(
+                HttpRequestMessage request,
+                CancellationToken cancellationToken
+            )
+            {
+                return Task.FromResult(_server(request));
+            }
+        }
+    }
+}