Tests: xUnit project with HAR fixtures (50 tests); fix relative delivery/HLS URLs resolving to file:// on Linux

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Jellyfin.Plugin.Floatplane.Tests/FakeHttp.cs

@@ -0,0 +1,66 @@
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Jellyfin.Plugin.Floatplane.Tests;
+
+/// <summary>Maps request URLs (prefix match on path, or a predicate) to canned responses and records requests.</summary>
+internal sealed class FakeHttpHandler : HttpMessageHandler
+{
+    private readonly List<(Func<HttpRequestMessage, bool> Match, Func<HttpRequestMessage, HttpResponseMessage> Respond)> _routes = new();
+
+    public List<HttpRequestMessage> Requests { get; } = new();
+
+    public FakeHttpHandler On(string pathPrefix, Func<HttpRequestMessage, HttpResponseMessage> respond)
+    {
+        _routes.Add((r => r.RequestUri!.AbsolutePath.StartsWith(pathPrefix, StringComparison.Ordinal), respond));
+        return this;
+    }
+
+    public FakeHttpHandler On(Func<HttpRequestMessage, bool> match, Func<HttpRequestMessage, HttpResponseMessage> respond)
+    {
+        _routes.Add((match, respond));
+        return this;
+    }
+
+    public static HttpResponseMessage Json(string body, HttpStatusCode status = HttpStatusCode.OK)
+        => new(status) { Content = new StringContent(body, System.Text.Encoding.UTF8, "application/json") };
+
+    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        Requests.Add(request);
+        foreach (var (match, respond) in _routes)
+        {
+            if (match(request))
+            {
+                var response = respond(request);
+                response.RequestMessage = request;
+                return Task.FromResult(response);
+            }
+        }
+
+        var notFound = new HttpResponseMessage(HttpStatusCode.NotFound) { RequestMessage = request, Content = new StringContent("no route for " + request.RequestUri) };
+        return Task.FromResult(notFound);
+    }
+}
+
+/// <summary>Mirrors the registrator: one named client with the plugin User-Agent.</summary>
+internal sealed class FakeHttpClientFactory : IHttpClientFactory
+{
+    private readonly HttpMessageHandler _handler;
+
+    public FakeHttpClientFactory(HttpMessageHandler handler)
+    {
+        _handler = handler;
+    }
+
+    public HttpClient CreateClient(string name)
+    {
+        var client = new HttpClient(_handler, disposeHandler: false);
+        client.DefaultRequestHeaders.UserAgent.ParseAdd(Plugin.UserAgent);
+        return client;
+    }
+}