Add unit tests for OutputTemplateRenderer for new UtcTimestamp token (TDD)

Addresses #164

Author: ManuelRin

test/Serilog.Sinks.Console.Tests/Output/OutputTemplateRendererTests.cs

@@ -400,4 +400,28 @@ public void TraceAndSpanAreIncludedWhenPresent()
         formatter.Format(evt, sw);
         Assert.Equal($"{traceId}/{spanId}", sw.ToString());
     }
+
+    [Fact]
+    public void TimestampTokenRendersLocalTime()
+    {
+        var logTimestampWithTimeZoneOffset = DateTimeOffset.Parse("2024-09-03T14:15:16.079+02:00", CultureInfo.InvariantCulture);
+        var formatter = new OutputTemplateRenderer(ConsoleTheme.None, "{Timestamp:yyyy-MM-dd HH:mm:ss}", CultureInfo.InvariantCulture);
+        var evt = new LogEvent(logTimestampWithTimeZoneOffset, LogEventLevel.Information, null, MessageTemplate.Empty, Array.Empty<LogEventProperty>());
+        var sw = new StringWriter();
+        formatter.Format(evt, sw);
+        // expect time in local time, unchanged from the input, the +02:00 offset should not affect the output
+        Assert.Equal("2024-09-03 14:15:16", sw.ToString());
+    }
+
+    [Fact]
+    public void UtcTimestampTokenRendersUtcTime()
+    {
+        var logTimestampWithTimeZoneOffset = DateTimeOffset.Parse("2024-09-03T14:15:16.079+02:00", CultureInfo.InvariantCulture);
+        var formatter = new OutputTemplateRenderer(ConsoleTheme.None, "{UtcTimestamp:yyyy-MM-dd HH:mm:ss}", CultureInfo.InvariantCulture);
+        var evt = new LogEvent(logTimestampWithTimeZoneOffset, LogEventLevel.Information, null, MessageTemplate.Empty, Array.Empty<LogEventProperty>());
+        var sw = new StringWriter();
+        formatter.Format(evt, sw);
+        // expect time in UTC, the +02:00 offset must be applied to adjust the hour
+        Assert.Equal("2024-09-03 12:15:16", sw.ToString());
+    }
 }