[Identity][Infrastructure] Improve test reliability (#13646)

* Catches HttpClient exceptions and retries on IdentityUI_ScriptTags_SubresourceIntegrityCheck and IdentityUI_ScriptTags_FallbackSourceContent_Matches_CDNContent

src/Identity/test/Identity.Test/IdentityUIScriptsTest.cs

@@ -9,7 +9,6 @@ using System.IO;
 using System.Linq;
 using System.Net.Http;
 using System.Security.Cryptography;
-using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Testing;
 using Xunit;
@@ -26,7 +25,7 @@ namespace Microsoft.AspNetCore.Identity.Test
         public IdentityUIScriptsTest(ITestOutputHelper output)
         {
             _output = output;
-            _httpClient = new HttpClient(new RetryHandler(new HttpClientHandler() { }));
+            _httpClient = new HttpClient(new RetryHandler(new HttpClientHandler() { }, output, TimeSpan.FromSeconds(1), 5));
         }
 
         public static IEnumerable<object[]> ScriptWithIntegrityData
@@ -188,25 +187,5 @@ namespace Microsoft.AspNetCore.Identity.Test
 
             throw new InvalidOperationException($"Solution root could not be located using application root {applicationPath}.");
         }
-
-        class RetryHandler : DelegatingHandler
-        {
-            public RetryHandler(HttpMessageHandler innerHandler) : base(innerHandler) { }
-
-            protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
-            {
-                HttpResponseMessage result = null;
-                for (var i = 0; i < 10; i++)
-                {
-                    result = await base.SendAsync(request, cancellationToken);
-                    if (result.IsSuccessStatusCode)
-                    {
-                        return result;
-                    }
-                    await Task.Delay(1000);
-                }
-                return result;
-            }
-        }
     }
 }

src/Identity/test/Identity.Test/RetryHandler.cs

@@ -0,0 +1,65 @@
+// 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.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Identity.Test
+{
+    internal class RetryHandler : DelegatingHandler
+        {
+            private readonly ITestOutputHelper _output;
+            private readonly int _maxRetries;
+            private TimeSpan _waitIntervalBeforeRetry;
+
+            public RetryHandler(
+                HttpClientHandler httpClientHandler,
+                ITestOutputHelper output,
+                TimeSpan initialWaitTime,
+                int maxAttempts) : base(httpClientHandler)
+            {
+                _waitIntervalBeforeRetry = initialWaitTime;
+                _output = output;
+                _maxRetries = maxAttempts;
+            }
+
+            protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+            {
+                HttpResponseMessage result = null;
+                var url = request.RequestUri;
+                var method = request.Method;
+
+                for (var i = 0; i < _maxRetries; i++)
+                {
+                    try
+                    {
+                        _output.WriteLine($"Sending request '{method} - {url}' {i+1} attempt.");
+                        result = await base.SendAsync(request, cancellationToken);
+                        if (result.IsSuccessStatusCode)
+                        {
+                            return result;
+                        }
+                        else
+                        {
+                            _output.WriteLine($"Request '{method} - {url}' failed with {result.StatusCode}.");
+                        }
+                    }
+                    catch (Exception e)
+                    {
+                        _output.WriteLine($"Request '{method} - {url}' failed with {e.ToString()}");
+                    }
+                    finally
+                    {
+                        await Task.Delay(_waitIntervalBeforeRetry, cancellationToken);
+                        _waitIntervalBeforeRetry = _waitIntervalBeforeRetry * 2;
+                    }
+                }
+                
+                // Try one last time to show the actual error.
+                return await base.SendAsync(request, cancellationToken);
+            }
+        }
+}