Update SA1513 tests for attributed local functions

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp9/LayoutRules/SA1513CSharp9UnitTests.cs

@@ -1,8 +1,6 @@
 // Copyright (c) Tunnel Vision Laboratories, LLC. All Rights Reserved.
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 
-#nullable disable
-
 namespace StyleCop.Analyzers.Test.CSharp9.LayoutRules
 {
     using System.Threading;
@@ -65,5 +63,43 @@ public int X
                 ReferenceAssemblies = ReferenceAssemblies.Net.Net50,
             }.RunAsync(CancellationToken.None).ConfigureAwait(false);
         }
+
+        [Fact]
+        [WorkItem(3978, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3978")]
+        public async Task TestLocalFunctionRequiresBlankLineAsync()
+        {
+            var testCode = @"using System;
+
+class TestClass
+{
+    void Outer()
+    {
+        [Obsolete]
+        void Local()
+        {
+        }{|#0:
+|}        int value = 0;
+    }
+}
+";
+
+            var fixedCode = @"using System;
+
+class TestClass
+{
+    void Outer()
+    {
+        [Obsolete]
+        void Local()
+        {
+        }
+
+        int value = 0;
+    }
+}
+";
+
+            await VerifyCSharpFixAsync(testCode, Diagnostic().WithLocation(0), fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }