Add test for http://dartbug.com/51527

Test currently fails on both DDC and dart2js

Bug: 51527
Change-Id: I229d5c9ba518d3323f98312f13740711523439e9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/290350
Reviewed-by: Mark Zhou <markzipan@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

tests/web/regress/issue/51527_test.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2023, 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.
+
+// Regression test for http://dartbug.com/51527
+
+import 'package:expect/expect.dart';
+
+void noop() {}
+dynamic makeNull() => null;
+
+String test(String? o) {
+  switch (o) {
+    case null:
+      return 'NULL';
+    case 'one':
+      return '1';
+    default:
+      return o;
+  }
+}
+
+void main() {
+  final String? s1 = 'one';
+  final String? s2 = 'two';
+  final String? s3 = Function.apply(makeNull, []);
+  final String? s4 = Function.apply(noop, []);
+
+  Expect.equals('1', test(s1));
+  Expect.equals('two', test(s2));
+  Expect.equals('NULL', test(s3));
+  Expect.equals('NULL', test(s4));
+}

tests/web_2/regress/issue/51527_test.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2023, 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.
+
+// Regression test for http://dartbug.com/51527
+
+import 'package:expect/expect.dart';
+
+void noop() {}
+dynamic makeNull() => null;
+
+String test(String o) {
+  switch (o) {
+    case null:
+      return 'NULL';
+    case 'one':
+      return '1';
+    default:
+      return o;
+  }
+}
+
+void main() {
+  final String s1 = 'one';
+  final String s2 = 'two';
+  final String s3 = Function.apply(makeNull, []);
+  final String s4 = Function.apply(noop, []);
+
+  Expect.equals('1', test(s1));
+  Expect.equals('two', test(s2));
+  Expect.equals('NULL', test(s3));
+  Expect.equals('NULL', test(s4));
+}