Test pooling diagnostic fixes. (#14349)

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>
Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>

Content.IntegrationTests/PoolTestLogHandler.cs

@@ -0,0 +1,75 @@
+using System;
+using System.IO;
+using NUnit.Framework;
+using Robust.Shared.Log;
+using Robust.Shared.Timing;
+using Serilog.Events;
+
+namespace Content.IntegrationTests;
+
+#nullable enable
+
+/// <summary>
+/// Log handler intended for pooled integration tests.
+/// </summary>
+/// <remarks>
+/// <para>
+/// This class logs to two places: an NUnit <see cref="TestContext"/>
+/// (so it nicely gets attributed to a test in your IDE),
+/// and an in-memory ring buffer for diagnostic purposes.
+/// If test pooling breaks, the ring buffer can be used to see what the broken instance has gone through.
+/// </para>
+/// <para>
+/// The active test context can be swapped out so pooled instances can correctly have their logs attributed.
+/// </para>
+/// </remarks>
+public sealed class PoolTestLogHandler : ILogHandler
+{
+    private readonly string? _prefix;
+
+    private RStopwatch _stopwatch;
+
+    public TextWriter? ActiveContext { get; private set; }
+
+    public LogLevel? FailureLevel { get; set; }
+
+    public PoolTestLogHandler(string? prefix)
+    {
+        _prefix = prefix != null ? $"{prefix}: " : "";
+    }
+
+    public void Log(string sawmillName, LogEvent message)
+    {
+        if (ActiveContext is not { } testContext)
+        {
+            // If this gets hit it means something is logging to this instance while it's "between" tests.
+            // This is a bug in either the game or the testing system, and must always be investigated.
+            throw new InvalidOperationException("Log to pool test log handler without active test context");
+        }
+
+        var level = message.Level.ToRobust();
+        var name = LogMessage.LogLevelToName(level);
+        var seconds = _stopwatch.Elapsed.TotalSeconds;
+        var rendered = message.RenderMessage();
+        var line = $"{_prefix}{seconds:F3}s [{name}] {sawmillName}: {rendered}";
+
+        testContext.WriteLine(line);
+
+        if (FailureLevel == null || level < FailureLevel)
+            return;
+
+        testContext.Flush();
+        Assert.Fail($"{line} Exception: {message.Exception}");
+    }
+
+    public void ClearContext()
+    {
+        ActiveContext = null;
+    }
+
+    public void ActivateContext(TextWriter context)
+    {
+        _stopwatch.Restart();
+        ActiveContext = context;
+    }
+}