Avoid flakiness in template tests around URL validity checking (#59195)

Author: SteveSandersonMS

src/ProjectTemplates/Shared/AspNetProcess.cs

@@ -171,12 +171,19 @@ public async Task ContainsLinks(Page page)
             else
             {
                 Assert.True(string.Equals(anchor.Href, expectedLink), $"Expected next link to be {expectedLink} but it was {anchor.Href}.");
-                var result = await RetryHelper.RetryRequest(async () =>
+
+                if (!string.Equals(anchor.Protocol, "https:") || string.Equals(anchor.HostName, "localhost", StringComparison.OrdinalIgnoreCase))
                 {
-                    return await _httpClient.GetAsync(anchor.Href);
-                }, logger: NullLogger.Instance);
+                    // This is a relative or same-site URI, so verify it goes to a real destination within the app.
+                    // We don't do this for external (absolute) URIs as it would introduce flakiness, and the code
+                    // above already checks that the URI is what we expect.
+                    var result = await RetryHelper.RetryRequest(async () =>
+                    {
+                        return await _httpClient.GetAsync(anchor.Href);
+                    }, logger: NullLogger.Instance);
 
-                Assert.True(IsSuccessStatusCode(result), $"{anchor.Href} is a broken link!");
+                    Assert.True(IsSuccessStatusCode(result), $"{anchor.Href} is a broken link!");
+                }
             }
         }
     }