Retain fake worker fault diagnostics in test fixtures

src/ZB.MOM.WW.MxGateway.Tests/Gateway/Workers/FakeWorkerDiagnosticsTests.cs

@@ -0,0 +1,88 @@
+using Microsoft.Extensions.Logging;
+using ZB.MOM.WW.MxGateway.Server.Workers;
+using ZB.MOM.WW.MxGateway.Tests.TestSupport;
+
+namespace ZB.MOM.WW.MxGateway.Tests.Gateway.Workers;
+
+/// <summary>Protects bounded teardown, fault observation, and safe diagnostic output.</summary>
+public sealed class FakeWorkerDiagnosticsTests
+{
+    /// <summary>Repeated gateway logs remain bounded and never format sensitive state or messages.</summary>
+    [Fact]
+    public void Log_WhenFaultsRepeat_ReportsOnlyBoundedMetadata()
+    {
+        using FakeWorkerDiagnostics diagnostics = new();
+        List<string> output = [];
+        diagnostics.SetOutput(output.Add);
+        for (int i = 0; i < 32; i++)
+        {
+            diagnostics.Log(LogLevel.Warning, new EventId(1), "secret-command",
+                new WorkerFrameProtocolException(WorkerFrameProtocolErrorCode.InvalidEnvelope, "secret-item"),
+                (state, exception) => $"{state} {exception}");
+        }
+
+        Assert.NotEmpty(output);
+        Assert.InRange(output.Count, 1, 16);
+        Assert.All(output, line =>
+        {
+            Assert.Contains("type=WorkerFrameProtocolException", line);
+            Assert.Contains("code=InvalidEnvelope", line);
+            Assert.DoesNotContain("secret", line);
+        });
+    }
+
+    /// <summary>A late fault is observed after timeout without calling the completed output sink.</summary>
+    /// <returns>The asynchronous test operation.</returns>
+    [Fact]
+    public async Task DrainAsync_WhenWorkerOutlivesBudget_ObservesLateFaultWithoutLateOutput()
+    {
+        FakeWorkerDiagnostics diagnostics = new();
+        List<string> output = [];
+        diagnostics.SetOutput(output.Add);
+        TaskCompletionSource worker = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        diagnostics.Track(worker.Task);
+        await diagnostics.DrainAsync(TimeSpan.Zero);
+        Assert.Contains(output, line => line.Contains("source=teardown") && line.Contains("type=TimeoutException"));
+        int beforeFault = output.Count;
+        worker.SetException(new WorkerFrameProtocolException(WorkerFrameProtocolErrorCode.InvalidEnvelope, "secret-item"));
+        await diagnostics.DrainAsync(TimeSpan.FromSeconds(5));
+        Assert.Equal(beforeFault, output.Count);
+    }
+
+    /// <summary>Expected cancellation does not add fault diagnostics.</summary>
+    /// <returns>The asynchronous test operation.</returns>
+    [Fact]
+    public async Task DrainAsync_WhenWorkerIsCancelled_DoesNotReportFault()
+    {
+        FakeWorkerDiagnostics diagnostics = new();
+        List<string> output = [];
+        diagnostics.SetOutput(output.Add);
+        diagnostics.Track(Task.FromCanceled(new CancellationToken(true)));
+        await diagnostics.DrainAsync(TimeSpan.FromSeconds(5));
+        Assert.Empty(output);
+    }
+
+    /// <summary>An unavailable output helper cannot fault the observer or replace the primary failure.</summary>
+    /// <returns>The asynchronous test operation.</returns>
+    [Fact]
+    public async Task DrainAsync_WhenOutputThrows_PreservesPrimaryFailure()
+    {
+        InvalidOperationException primary = new("primary");
+        FakeWorkerDiagnostics diagnostics = new();
+        diagnostics.SetOutput(_ => throw new InvalidOperationException("completed output"));
+        Exception? failure = await Record.ExceptionAsync(async () =>
+        {
+            try
+            {
+                throw primary;
+            }
+            finally
+            {
+                diagnostics.Track(Task.FromException(new WorkerFrameProtocolException(
+                    WorkerFrameProtocolErrorCode.InvalidEnvelope, "secret-item")));
+                await diagnostics.DrainAsync(TimeSpan.FromSeconds(5));
+            }
+        });
+        Assert.Same(primary, failure);
+    }
+}