part #2

src/__Libraries/__Tests/StellaOps.Replay.Tests/FeedSnapshotLoaderTests.cs

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+using FluentAssertions;
+using Microsoft.Extensions.Logging.Abstractions;
+using StellaOps.Replay.Loaders;
+using StellaOps.TestKit;
+using Xunit;
+
+namespace StellaOps.Replay.Tests;
+
+public sealed class FeedSnapshotLoaderTests
+{
+    [Trait("Category", TestCategories.Unit)]
+    [Fact]
+    public async Task LoadByDigestAsync_InvalidDigest_ThrowsFormatException()
+    {
+        var loader = new FeedSnapshotLoader(new FeedStorageStub(null), NullLogger<FeedSnapshotLoader>.Instance);
+        var digest = SnapshotTestData.CreateInvalidDigest('a');
+
+        var action = () => loader.LoadByDigestAsync(digest);
+
+        await action.Should().ThrowAsync<FormatException>();
+    }
+
+    [Trait("Category", TestCategories.Unit)]
+    [Fact]
+    public async Task LoadByDigestAsync_ShortDigest_ThrowsFormatException()
+    {
+        var loader = new FeedSnapshotLoader(new FeedStorageStub(null), NullLogger<FeedSnapshotLoader>.Instance);
+        var digest = new string('a', 63);
+
+        var action = () => loader.LoadByDigestAsync(digest);
+
+        await action.Should().ThrowAsync<FormatException>();
+    }
+
+    [Trait("Category", TestCategories.Unit)]
+    [Fact]
+    public async Task LoadByDigestAsync_DigestMismatch_ThrowsException()
+    {
+        var snapshot = SnapshotTestData.CreateFeedSnapshot(SnapshotTestData.CreateValidDigest('b'));
+        var actualDigest = SnapshotTestData.ComputeDigest(snapshot);
+        var expectedDigest = SnapshotTestData.CreateDifferentDigest(actualDigest);
+        var loader = new FeedSnapshotLoader(new FeedStorageStub(snapshot), NullLogger<FeedSnapshotLoader>.Instance);
+
+        var action = () => loader.LoadByDigestAsync(expectedDigest);
+
+        await action.Should().ThrowAsync<DigestMismatchException>();
+    }
+}