Logged .NET events with the time they happened (#1042)

app/Tests/Tools/TerminalLoggerTests.cs

@@ -0,0 +1,48 @@
+using System.Globalization;
+
+using AIStudio.Tools;
+
+namespace AIStudio.Tests.Tools;
+
+/// <summary>
+/// Pins the format in which log events travel to the Rust runtime.
+/// </summary>
+/// <remarks>
+/// The Rust runtime reads this format to log each event with the time it happened. Its tests in
+/// runtime/src/log.rs parse the same text, so both sides have to change together.
+/// </remarks>
+[TestFixture]
+public sealed class TerminalLoggerTests
+{
+    private const string TRANSPORT_TIMESTAMP = "2026-10-09T17:53:54.5629130+00:00";
+
+    private static readonly DateTimeOffset EVENT_TIME = new DateTimeOffset(2026, 10, 9, 17, 53, 54, TimeSpan.Zero).AddTicks(5_629_130);
+
+    [Test]
+    public void TheTransportTimestampIsPinned()
+    {
+        Assert.That(TerminalLogger.FormatTransportTimestamp(EVENT_TIME), Is.EqualTo(TRANSPORT_TIMESTAMP));
+    }
+
+    [Test]
+    public void TheTransportTimestampIgnoresTheCurrentCulture()
+    {
+        var culture = (CultureInfo)CultureInfo.InvariantCulture.Clone();
+        culture.DateTimeFormat.TimeSeparator = ".";
+
+        var previousCulture = CultureInfo.CurrentCulture;
+        try
+        {
+            CultureInfo.CurrentCulture = culture;
+            Assert.Multiple(() =>
+            {
+                Assert.That(EVENT_TIME.ToString("yyyy-MM-dd HH:mm:ss.fff"), Is.EqualTo("2026-10-09 17.53.54.562"), "The format sent before followed the time separator of the current culture.");
+                Assert.That(TerminalLogger.FormatTransportTimestamp(EVENT_TIME), Is.EqualTo(TRANSPORT_TIMESTAMP));
+            });
+        }
+        finally
+        {
+            CultureInfo.CurrentCulture = previousCulture;
+        }
+    }
+}