Refactor code structure for improved readability and maintainability; removed redundant code blocks and optimized function calls.

src/Attestor/StellaOps.Attestation.Tests/DsseHelperTests.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Text;
+using System.Text.Json;
+using System.Threading.Tasks;
+using FluentAssertions;
+using StellaOps.Attestation;
+using StellaOps.Attestor.Envelope;
+using Xunit;
+
+public class DsseHelperTests
+{
+    private sealed class FakeSigner : IAuthoritySigner
+    {
+        public Task<string> GetKeyIdAsync(System.Threading.CancellationToken cancellationToken = default)
+            => Task.FromResult("fake-key");
+
+        public Task<byte[]> SignAsync(ReadOnlyMemory<byte> paePayload, System.Threading.CancellationToken cancellationToken = default)
+            => Task.FromResult(Convert.FromHexString("deadbeef"));
+    }
+
+    [Fact]
+    public async Task WrapAsync_ProducesDsseEnvelope()
+    {
+        var stmt = new InTotoStatement(
+            Type: "https://in-toto.io/Statement/v1",
+            Subject: new[] { new Subject("demo", new System.Collections.Generic.Dictionary<string, string> { { "sha256", "abcd" } }) },
+            PredicateType: "demo/predicate",
+            Predicate: new { hello = "world" });
+
+        var envelope = await DsseHelper.WrapAsync(stmt, new FakeSigner());
+
+        envelope.PayloadType.Should().Be("https://in-toto.io/Statement/v1");
+        var roundtrip = JsonSerializer.Deserialize<InTotoStatement>(envelope.Payload.Span);
+        roundtrip!.PredicateType.Should().Be("demo/predicate");
+        envelope.Signatures.Should().ContainSingle();
+        envelope.Signatures[0].KeyId.Should().Be("fake-key");
+        envelope.Signatures[0].Signature.Should().Be(Convert.ToBase64String(Convert.FromHexString("deadbeef")));
+    }
+
+    [Fact]
+    public void PreAuthenticationEncoding_FollowsDsseSpec()
+    {
+        var payloadType = "example/type";
+        var payload = Encoding.UTF8.GetBytes("{}");
+
+        var pae = DsseHelper.PreAuthenticationEncoding(payloadType, payload);
+        pae.Should().ContainSubsequence(Encoding.UTF8.GetBytes(payloadType));
+        pae.Should().ContainSubsequence(payload);
+    }
+}