Language test for unnamed-libraries

Bug: dart-lang/language#1073
Change-Id: I9d57c86c35b5712029c610197e6ad823d34c492e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/262580
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Erik Ernst <[email protected]>

Author: srawlins

tests/language/library/unnamed_library_test.dart

@@ -0,0 +1,11 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code as governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--enable-experiment=unnamed-libraries
+
+/// Doc comment.
+@deprecated
+library;
+
+main() {}