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/ProxySignatureTests.cs

@@ -0,0 +1,51 @@
+using Jellyfin.Plugin.Floatplane.Api;
+using Xunit;
+
+namespace Jellyfin.Plugin.Floatplane.Tests;
+
+public class ProxySignatureTests
+{
+    [Fact]
+    public void Create_Verify_roundtrip()
+    {
+        var sig = ProxySignature.Create("hls", "post1", "video1", "1080");
+
+        Assert.Equal(64, sig.Length);
+        Assert.True(ProxySignature.Verify(sig, "hls", "post1", "video1", "1080"));
+        Assert.Equal(sig, ProxySignature.Create("hls", "post1", "video1", "1080"));
+    }
+
+    [Fact]
+    public void Tampered_parts_or_signature_fail()
+    {
+        var sig = ProxySignature.Create("hls", "post1", "video1", "1080");
+
+        Assert.False(ProxySignature.Verify(sig, "hls", "post1", "video1", "2160"));
+        Assert.False(ProxySignature.Verify(sig, "mp4", "post1", "video1", "1080"));
+        Assert.False(ProxySignature.Verify(sig[..^1] + (sig[^1] == 'a' ? 'b' : 'a'), "hls", "post1", "video1", "1080"));
+        Assert.False(ProxySignature.Verify(null, "hls", "post1", "video1", "1080"));
+        Assert.False(ProxySignature.Verify(string.Empty, "hls", "post1", "video1", "1080"));
+    }
+
+    [Theory]
+    [InlineData("https://www.floatplane.com/api/video/watchKey?token=abc")]
+    [InlineData("https://cdn-vod-drm2.floatplane.com/Videos/x/1080.mp4/chunk.m3u8?token=a.b.c&x=y%20z")]
+    [InlineData("å ä ö")]
+    public void EncodeUrl_DecodeUrl_roundtrip(string value)
+    {
+        var encoded = ProxySignature.EncodeUrl(value);
+
+        Assert.DoesNotContain('+', encoded);
+        Assert.DoesNotContain('/', encoded);
+        Assert.DoesNotContain('=', encoded);
+        Assert.Equal(value, ProxySignature.DecodeUrl(encoded));
+    }
+
+    [Fact]
+    public void DecodeUrl_rejects_garbage()
+    {
+        Assert.Null(ProxySignature.DecodeUrl(null));
+        Assert.Null(ProxySignature.DecodeUrl(string.Empty));
+        Assert.Null(ProxySignature.DecodeUrl("!!!not base64!!!"));
+    }
+}