Expand test coverage to match specs

GameList.Tests/HelperTests.cs

@@ -1,13 +1,18 @@
 using System.Net;
+using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Reflection;
 using GameList.Infrastructure;
 using GameList.Endpoints;
 using GameList.Tests.Support;
+using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.FileProviders;
 using System.Linq;
+using Microsoft.AspNetCore.Mvc.Testing;
+using System.Text.Json;
+using System.Net.Http.Json;
 
 namespace GameList.Tests;
 
@@ -62,6 +67,74 @@ public class HelperTests
         Assert.False(await EndpointHelpers.IsReachableImageAsync("http://127.0.0.1/img.png", new StubHttpClientFactory(new StubHttpMessageHandler())));
     }
 
+    [Fact]
+    public async Task IsReachableImageAsync_handles_head_success_redirect_and_size_guard()
+    {
+        var handler = new StubHttpMessageHandler();
+        handler.SetResponder(req =>
+        {
+            if (req.Method == HttpMethod.Head)
+            {
+                var resp = new HttpResponseMessage(HttpStatusCode.OK);
+                resp.Content = new ByteArrayContent(Array.Empty<byte>());
+                resp.Content.Headers.ContentType = new MediaTypeHeaderValue("image/png");
+                resp.Content.Headers.ContentLength = 100;
+                return resp;
+            }
+            return new HttpResponseMessage(HttpStatusCode.OK)
+            {
+                Content = new ByteArrayContent(Array.Empty<byte>())
+                {
+                    Headers =
+                    {
+                        ContentType = new MediaTypeHeaderValue("image/png"),
+                        ContentLength = 100
+                    }
+                }
+            };
+        });
+
+        var ok = await EndpointHelpers.IsReachableImageAsync("http://example.com/img.png", new StubHttpClientFactory(handler), handler);
+        Assert.True(ok);
+
+        handler.SetResponder(_ =>
+        {
+            var resp = new HttpResponseMessage(HttpStatusCode.Redirect);
+            resp.Headers.Location = new Uri("http://example.com/other");
+            return resp;
+        });
+        var redirect = await EndpointHelpers.IsReachableImageAsync("http://example.com/img.png", new StubHttpClientFactory(handler), handler);
+        Assert.False(redirect);
+
+        handler.SetResponder(_ =>
+        {
+            var resp = new HttpResponseMessage(HttpStatusCode.OK);
+            resp.Content = new ByteArrayContent(new byte[10]);
+            resp.Content.Headers.ContentType = new MediaTypeHeaderValue("image/png");
+            resp.Content.Headers.ContentLength = 6 * 1024 * 1024; // over 5 MB
+            return resp;
+        });
+        var tooLarge = await EndpointHelpers.IsReachableImageAsync("http://example.com/img.png", new StubHttpClientFactory(handler), handler);
+        Assert.False(tooLarge);
+    }
+
+    [Fact]
+    public async Task IsReachableImageAsync_rejects_non_image_content()
+    {
+        var handler = new StubHttpMessageHandler();
+        handler.SetResponder(_ =>
+        {
+            var resp = new HttpResponseMessage(HttpStatusCode.OK);
+            resp.Content = new ByteArrayContent(System.Text.Encoding.UTF8.GetBytes("not image"));
+            resp.Content.Headers.ContentType = new MediaTypeHeaderValue("text/plain");
+            resp.Content.Headers.ContentLength = 9;
+            return resp;
+        });
+
+        var result = await EndpointHelpers.IsReachableImageAsync("http://example.com/img.png", new StubHttpClientFactory(handler), handler);
+        Assert.False(result);
+    }
+
     [Fact]
     public void Link_root_helpers_handle_groups()
     {
@@ -98,6 +171,29 @@ public class HelperTests
         Assert.Equal(3, root); // cycle breaks on revisit
     }
 
+    [Fact]
+    public async Task Global_exception_handler_returns_json_error()
+    {
+        using var factory = new TestWebApplicationFactory().WithWebHostBuilder(builder =>
+        {
+            builder.Configure(app =>
+            {
+                app.UseGlobalExceptionLogging();
+                app.UseRouting();
+                app.UseEndpoints(endpoints =>
+                {
+                    endpoints.MapGet("/boom", _ => throw new InvalidOperationException("boom"));
+                });
+            });
+        });
+
+        var client = factory.CreateClient();
+        var resp = await client.GetAsync("/boom");
+        Assert.Equal(HttpStatusCode.InternalServerError, resp.StatusCode);
+        var json = await resp.Content.ReadFromJsonAsync<JsonElement>();
+        Assert.Equal("Unexpected server error", json.GetProperty("error").GetString());
+    }
+
     private class FakeEnv : IWebHostEnvironment
     {
         public string ApplicationName { get; set; } = "";