Add missing nullable DateTime comparison tests for INTL0202

Add test coverage for DateTime? compared against DateTimeOffset and
DateTimeOffset? in binary comparison expressions, which were previously
untested edge cases.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: BenjaminMichaelis

IntelliTect.Analyzer/IntelliTect.Analyzer.Test/DateTimeConversionTests.cs

@@ -339,6 +339,86 @@ static void Main(string[] args)
                            });
         }
 
+        [TestMethod]
+        public void NullableDateTimeToDateTimeOffsetComparison_ProducesWarningMessage()
+        {
+            string source = @"
+using System;
+using System.Threading;
+
+namespace ConsoleApp1
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            DateTime? first = DateTime.Now;
+
+            Thread.Sleep(10);
+
+            DateTimeOffset second = DateTimeOffset.Now;
+
+            if (first < second)
+            {
+                Console.WriteLine(""Time has passed..."");
+            }
+        }
+    }
+}";
+
+            VerifyCSharpDiagnostic(source,
+                           new DiagnosticResult
+                           {
+                               Id = "INTL0202",
+                               Severity = DiagnosticSeverity.Warning,
+                               Message = "Using 'DateTimeOffset.implicit operator DateTimeOffset(DateTime)' or 'new DateTimeOffset(DateTime)' can result in unpredictable behavior",
+                               Locations =
+                                   [
+                            new DiagnosticResultLocation("Test0.cs", 17, 17)
+                                   ]
+                           });
+        }
+
+        [TestMethod]
+        public void NullableDateTimeToNullableDateTimeOffsetComparison_ProducesWarningMessage()
+        {
+            string source = @"
+using System;
+using System.Threading;
+
+namespace ConsoleApp1
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            DateTime? first = DateTime.Now;
+
+            Thread.Sleep(10);
+
+            DateTimeOffset? second = DateTimeOffset.Now;
+
+            if (first < second)
+            {
+                Console.WriteLine(""Time has passed..."");
+            }
+        }
+    }
+}";
+
+            VerifyCSharpDiagnostic(source,
+                           new DiagnosticResult
+                           {
+                               Id = "INTL0202",
+                               Severity = DiagnosticSeverity.Warning,
+                               Message = "Using 'DateTimeOffset.implicit operator DateTimeOffset(DateTime)' or 'new DateTimeOffset(DateTime)' can result in unpredictable behavior",
+                               Locations =
+                                   [
+                            new DiagnosticResultLocation("Test0.cs", 17, 17)
+                                   ]
+                           });
+        }
+
         protected override DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer()
         {
             return new Analyzers.BanImplicitDateTimeToDateTimeOffsetConversion();