Update SA1125 tests for native-sized integers

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp9/ReadabilityRules/SA1125CSharp9UnitTests.cs

@@ -3,9 +3,46 @@
 
 namespace StyleCop.Analyzers.Test.CSharp9.ReadabilityRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp8.ReadabilityRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopDiagnosticVerifier<StyleCop.Analyzers.ReadabilityRules.SA1125UseShorthandForNullableTypes>;
 
     public partial class SA1125CSharp9UnitTests : SA1125CSharp8UnitTests
     {
+        [Theory]
+        [InlineData("System.Nullable<nint>")]
+        [InlineData("Nullable<IntPtr>")]
+        [InlineData("System.Nullable<nuint>")]
+        [InlineData("Nullable<UIntPtr>")]
+        [WorkItem(3969, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3969")]
+        public async Task TestNativeSizedNullableTypesAsync(string nullableForm)
+        {
+            var testCode = @"
+using System;
+
+class TestClass
+{
+    {|#0:" + nullableForm + @"|} value;
+}";
+
+            await VerifyCSharpDiagnosticAsync(testCode, Diagnostic().WithLocation(0), CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3969, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3969")]
+        public async Task TestNativeSizedNullableAliasesDoNotReportAsync()
+        {
+            var testCode = @"
+class TestClass
+{
+    nint? nativeInt;
+    nuint? nativeUInt;
+}";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }