Test for #61222

Bug: #61222
Change-Id: I589c5f804bb24fe0c2983e637ba6e40422a194c7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/442941
Reviewed-by: Lasse Nielsen <[email protected]>
Commit-Queue: Stephen Adams <[email protected]>

Author: rakudrama

tests/language/regress/regress61222_test.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test for http://dartbug.com/61222.
+
+import 'package:expect/expect.dart';
+
+void main() {
+  var eList = <E>[?E.vn(), ?E.v1()];
+  Expect.listEquals([E.v1()], eList);
+}
+
+extension type const E._(int? _) {
+  const E.vn() : this._(null);
+  const E.v1() : this._(1);
+}