Unit tests for OutputTemplateRenderer for UtcTimestamp/Timestamp token enhanced

- round-trip standard format string added to tests
- for Timestamp the +00:00 format is expected, for UtcTimestamp the Z suffix is expected

Relates to #164

Author: ManuelRin

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

@@ -406,28 +406,44 @@ public void TimestampTokenRendersLocalTime()
     {
         var logTimestampWithTimeZoneOffset = DateTimeOffset.Parse("2024-09-03T14:15:16.079+02:00", CultureInfo.InvariantCulture);
         var formatter = new OutputTemplateRenderer(ConsoleTheme.None,
-            "Default Format: {Timestamp} / Custom Format String: {Timestamp:yyyy-MM-dd HH:mm:ss}",
+            """
+            Default Format: {Timestamp}
+            Round-trip Standard Format String: {Timestamp:o}
+            Custom Format String: {Timestamp:yyyy-MM-dd HH:mm:ss}
+            """,
             CultureInfo.InvariantCulture);
         var evt = new LogEvent(logTimestampWithTimeZoneOffset, LogEventLevel.Debug, null,
             new MessageTemplate(Enumerable.Empty<MessageTemplateToken>()), Enumerable.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("Default Format: 09/03/2024 14:15:16 +02:00 / Custom Format String: 2024-09-03 14:15:16", sw.ToString());
+        Assert.Equal("""
+                     Default Format: 09/03/2024 14:15:16 +02:00
+                     Round-trip Standard Format String: 2024-09-03T14:15:16.0790000+02:00
+                     Custom Format String: 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,
-            "Default Format: {UtcTimestamp} / Custom Format String: {UtcTimestamp:yyyy-MM-dd HH:mm:ss}",
+            """
+            Default Format: {UtcTimestamp}
+            Round-trip Standard Format String: {UtcTimestamp:o}
+            Custom Format String: {UtcTimestamp:yyyy-MM-dd HH:mm:ss}
+            """,
             CultureInfo.InvariantCulture);
         var evt = new LogEvent(logTimestampWithTimeZoneOffset, LogEventLevel.Debug, null,
             new MessageTemplate(Enumerable.Empty<MessageTemplateToken>()), Enumerable.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("Default Format: 09/03/2024 12:15:16 / Custom Format String: 2024-09-03 12:15:16", sw.ToString());
+        Assert.Equal("""
+                     Default Format: 09/03/2024 12:15:16
+                     Round-trip Standard Format String: 2024-09-03T12:15:16.0790000Z
+                     Custom Format String: 2024-09-03 12:15:16
+                     """, sw.ToString());
     }
 }