feat(health): SiteAuditBacklog metric (count + age + bytes) (#23 M6)

tests/ScadaLink.AuditLog.Tests/Site/SqliteAuditWriterBacklogStatsTests.cs

@@ -0,0 +1,136 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using ScadaLink.AuditLog.Site;
+using ScadaLink.Commons.Entities.Audit;
+using ScadaLink.Commons.Types.Enums;
+
+namespace ScadaLink.AuditLog.Tests.Site;
+
+/// <summary>
+/// Bundle E (M6-T6) tests for <see cref="SqliteAuditWriter.GetBacklogStatsAsync"/>.
+/// Exercises the health-metric surface that <c>SiteAuditBacklogReporter</c>
+/// polls every 30 s and pushes onto the site health report as
+/// <c>SiteAuditBacklog</c>.
+/// </summary>
+public class SqliteAuditWriterBacklogStatsTests : IDisposable
+{
+    private readonly string _dbPath;
+
+    public SqliteAuditWriterBacklogStatsTests()
+    {
+        // OnDiskBytes assertions only make sense against a real file — the
+        // shared-cache in-memory mode returns 0 for the file size, so this
+        // suite is opinionated about file-backed storage. Tests in
+        // SqliteAuditWriterWriteTests use in-memory for performance reasons.
+        _dbPath = Path.Combine(Path.GetTempPath(),
+            $"audit-backlog-stats-{Guid.NewGuid():N}.db");
+    }
+
+    public void Dispose()
+    {
+        if (File.Exists(_dbPath))
+        {
+            try { File.Delete(_dbPath); } catch { /* test cleanup best-effort */ }
+        }
+    }
+
+    private SqliteAuditWriter CreateWriter()
+    {
+        var options = new SqliteAuditWriterOptions { DatabasePath = _dbPath };
+        return new SqliteAuditWriter(
+            Options.Create(options),
+            NullLogger<SqliteAuditWriter>.Instance);
+    }
+
+    private static AuditEvent NewEvent(DateTime? occurredAtUtc = null) => new()
+    {
+        EventId = Guid.NewGuid(),
+        OccurredAtUtc = occurredAtUtc ?? DateTime.UtcNow,
+        Channel = AuditChannel.ApiOutbound,
+        Kind = AuditKind.ApiCall,
+        Status = AuditStatus.Delivered,
+        PayloadTruncated = false,
+    };
+
+    [Fact]
+    public async Task EmptyDb_Returns_Zero_Null_AndZeroBytes()
+    {
+        // No file exists yet — the writer ctor creates one but no rows are
+        // inserted; the snapshot should report a clean queue. OnDiskBytes is
+        // allowed to be zero (fresh ftruncate) OR small (page header) — the
+        // contract only requires non-negative; we assert >= 0 and exercise
+        // the pending fields strictly.
+        await using var writer = CreateWriter();
+
+        var snapshot = await writer.GetBacklogStatsAsync();
+
+        Assert.Equal(0, snapshot.PendingCount);
+        Assert.Null(snapshot.OldestPendingUtc);
+        Assert.True(snapshot.OnDiskBytes >= 0,
+            $"OnDiskBytes must be non-negative, got {snapshot.OnDiskBytes}");
+    }
+
+    [Fact]
+    public async Task Pending_5_Returns_5()
+    {
+        await using var writer = CreateWriter();
+
+        for (var i = 0; i < 5; i++)
+        {
+            await writer.WriteAsync(NewEvent());
+        }
+
+        var snapshot = await writer.GetBacklogStatsAsync();
+
+        Assert.Equal(5, snapshot.PendingCount);
+    }
+
+    [Fact]
+    public async Task OldestPending_Is_Earliest_OccurredAtUtc()
+    {
+        await using var writer = CreateWriter();
+
+        var t1 = new DateTime(2026, 5, 20, 10, 0, 0, DateTimeKind.Utc);
+        var t2 = new DateTime(2026, 5, 20, 10, 1, 0, DateTimeKind.Utc);
+        var t3 = new DateTime(2026, 5, 20, 10, 2, 0, DateTimeKind.Utc);
+
+        // Insert out of order so the snapshot is not "the last write" by
+        // accident — the OldestPendingUtc must come from a column-min, not
+        // an insertion-order proxy.
+        await writer.WriteAsync(NewEvent(t2));
+        await writer.WriteAsync(NewEvent(t1));
+        await writer.WriteAsync(NewEvent(t3));
+
+        var snapshot = await writer.GetBacklogStatsAsync();
+
+        Assert.Equal(3, snapshot.PendingCount);
+        Assert.NotNull(snapshot.OldestPendingUtc);
+        // The DB round-trips OccurredAtUtc through the "o" format which
+        // preserves Kind=Utc — assert tick-equality.
+        Assert.Equal(t1, snapshot.OldestPendingUtc!.Value);
+    }
+
+    [Fact]
+    public async Task OnDiskBytes_ReturnsFileSize()
+    {
+        await using var writer = CreateWriter();
+
+        // Insert enough rows to grow the file past the empty schema baseline.
+        for (var i = 0; i < 100; i++)
+        {
+            await writer.WriteAsync(NewEvent());
+        }
+
+        var snapshot = await writer.GetBacklogStatsAsync();
+
+        // The exact size depends on SQLite page allocation, but a file-backed
+        // db with 100 inserted rows MUST be larger than the empty schema
+        // (a few pages, ~4 KB). The implementation should return the
+        // FileInfo.Length value verbatim.
+        Assert.True(File.Exists(_dbPath), $"DB file should exist at {_dbPath}");
+        var expected = new FileInfo(_dbPath).Length;
+        Assert.Equal(expected, snapshot.OnDiskBytes);
+        Assert.True(snapshot.OnDiskBytes > 0,
+            $"after 100 inserts OnDiskBytes must be > 0, got {snapshot.OnDiskBytes}");
+    }
+}