Add SA1519 tests for extension foreach

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp9/LayoutRules/SA1519CSharp9UnitTests.cs

@@ -3,9 +3,84 @@
 
 namespace StyleCop.Analyzers.Test.CSharp9.LayoutRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp8.LayoutRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.LayoutRules.SA1519BracesMustNotBeOmittedFromMultiLineChildStatement,
+        StyleCop.Analyzers.LayoutRules.SA1503CodeFixProvider>;
 
     public partial class SA1519CSharp9UnitTests : SA1519CSharp8UnitTests
     {
+        [Fact]
+        [WorkItem(3976, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3976")]
+        public async Task TestForeachWithExtensionEnumeratorAsync()
+        {
+            var testCode = @"
+using System;
+
+public class TestClass
+{
+    public void TestMethod()
+    {
+        foreach (var value in new ExtensionEnumerable())
+            [|Console.WriteLine(
+                value);|]
+    }
+}
+
+public class ExtensionEnumerable
+{
+}
+
+public struct ExtensionEnumerator
+{
+    public int Current => 0;
+
+    public bool MoveNext() => false;
+}
+
+public static class ExtensionEnumerableExtensions
+{
+    public static ExtensionEnumerator GetEnumerator(this ExtensionEnumerable enumerable) => new();
+}
+";
+
+            var fixedCode = @"
+using System;
+
+public class TestClass
+{
+    public void TestMethod()
+    {
+        foreach (var value in new ExtensionEnumerable())
+        {
+            Console.WriteLine(
+                value);
+        }
+    }
+}
+
+public class ExtensionEnumerable
+{
+}
+
+public struct ExtensionEnumerator
+{
+    public int Current => 0;
+
+    public bool MoveNext() => false;
+}
+
+public static class ExtensionEnumerableExtensions
+{
+    public static ExtensionEnumerator GetEnumerator(this ExtensionEnumerable enumerable) => new();
+}
+";
+
+            await VerifyCSharpFixAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }